[interp] context can be uninitialized for get_resume_state callback

`jit_tls->interp_context` gets initialized lazily, that is, upon the first interpreter execution on a specific thread (e.g. via interp_runtime_invoke). However, with mixed mode the execution can purely happen in AOT code upon the first interaction with the managed debugger.

Stack trace:

```
  thread dotnet#1, name = 'tid_407', queue = 'com.apple.main-thread'
    frame #0: 0x0000000190aedc94 libsystem_kernel.dylib`__psynch_cvwait + 8
    frame dotnet#1: 0x0000000190a0f094 libsystem_pthread.dylib`_pthread_cond_wait$VARIANT$armv81 + 672
    frame dotnet#2: 0x000000010431318c reloadcontext.iOS`mono_os_cond_wait(cond=0x0000000104b9ba78, mutex=0x0000000104b9ba30) at mono-os-mutex.h:219:8
    frame dotnet#3: 0x0000000104312a68 reloadcontext.iOS`mono_coop_cond_wait(cond=0x0000000104b9ba78, mutex=0x0000000104b9ba30) at mono-coop-mutex.h:91:2
    frame dotnet#4: 0x0000000104312858 reloadcontext.iOS`suspend_current at debugger-agent.c:3021:4
    frame dotnet#5: 0x000000010431be18 reloadcontext.iOS`process_event(event=EVENT_KIND_BREAKPOINT, arg=0x0000000145d09ae8, il_offset=0, ctx=0x0000000149015c20, events=0x0000000000000000, suspend_policy=2) at debugger-agent.c:4058:3
    frame dotnet#6: 0x0000000104310cf4 reloadcontext.iOS`process_breakpoint_events(_evts=0x000000028351a680, method=0x0000000145d09ae8, ctx=0x0000000149015c20, il_offset=0) at debugger-agent.c:4722:3
    frame dotnet#7: 0x000000010432f1c8 reloadcontext.iOS`mono_de_process_breakpoint(void_tls=0x0000000149014e00, from_signal=0) at debugger-engine.c:1141:2
    frame dotnet#8: 0x000000010430f238 reloadcontext.iOS`debugger_agent_breakpoint_from_context(ctx=0x000000016f656790) at debugger-agent.c:4938:2
    frame dotnet#9: 0x00000001011b73a4 reloadcontext.iOS`sdb_breakpoint_trampoline + 148
    frame dotnet#10: 0x00000001008511b4 reloadcontext.iOS`reloadcontext_iOS_Application_Main_string__(args=0x000000010703a030) at Main.cs:14
    frame dotnet#11: 0x00000001010f9730 reloadcontext.iOS`wrapper_runtime_invoke_object_runtime_invoke_dynamic_intptr_intptr_intptr_intptr + 272
    frame dotnet#12: 0x00000001042fd8b8 reloadcontext.iOS`mono_jit_runtime_invoke(method=0x0000000145d09ae8, obj=0x0000000000000000, params=0x000000016f656f20, exc=0x0000000000000000, error=0x000000016f656ff8) at mini-runtime.c:3162:3
    frame dotnet#13: 0x0000000104411950 reloadcontext.iOS`do_runtime_invoke(method=0x0000000145d09ae8, obj=0x0000000000000000, params=0x000000016f656f20, exc=0x0000000000000000, error=0x000000016f656ff8) at object.c:3052:11
    frame dotnet#14: 0x000000010440c4dc reloadcontext.iOS`mono_runtime_invoke_checked(method=0x0000000145d09ae8, obj=0x0000000000000000, params=0x000000016f656f20, error=0x000000016f656ff8) at object.c:3220:9
    frame dotnet#15: 0x0000000104415ae0 reloadcontext.iOS`do_exec_main_checked(method=0x0000000145d09ae8, args=0x000000010703a030, error=0x000000016f656ff8) at object.c:5184:3
    frame dotnet#16: 0x00000001044144ac reloadcontext.iOS`mono_runtime_exec_main_checked(method=0x0000000145d09ae8, args=0x000000010703a030, error=0x000000016f656ff8) at object.c:5281:9
    frame dotnet#17: 0x0000000104414500 reloadcontext.iOS`mono_runtime_run_main_checked(method=0x0000000145d09ae8, argc=1, argv=0x000000016f6570d0, error=0x000000016f656ff8) at object.c:4734:9
    frame dotnet#18: 0x00000001042d3b54 reloadcontext.iOS`mono_jit_exec_internal(domain=0x0000000145f00130, assembly=0x0000000281ba2900, argc=1, argv=0x000000016f6570d0) at driver.c:1320:13
    frame dotnet#19: 0x00000001042d39a4 reloadcontext.iOS`mono_jit_exec(domain=0x0000000145f00130, assembly=0x0000000281ba2900, argc=1, argv=0x000000016f6570d0) at driver.c:1265:7
    frame dotnet#20: 0x0000000104597994 reloadcontext.iOS`::xamarin_main(argc=5, argv=0x000000016f657a80, launch_mode=XamarinLaunchModeApp) at monotouch-main.m:483:8
    frame dotnet#21: 0x00000001008510dc reloadcontext.iOS`main(argc=5, argv=0x000000016f657a80) at main.m:104:11
    frame dotnet#22: 0x0000000190af8360 libdyld.dylib`start + 4
[...]
* thread dotnet#5, name = 'Debugger agent', stop reason = signal SIGABRT
  * frame #0: 0x0000000190aedec4 libsystem_kernel.dylib`__pthread_kill + 8
    frame dotnet#1: 0x0000000190a0d724 libsystem_pthread.dylib`pthread_kill$VARIANT$armv81 + 216
    frame dotnet#2: 0x000000019095d844 libsystem_c.dylib`abort + 100
    frame dotnet#3: 0x00000001045871b4 reloadcontext.iOS`log_callback(log_domain=0x0000000000000000, log_level="error", message="* Assertion at ../../../../../mono/mini/interp/interp.c:7176, condition `context' not met\n", fatal=4, user_data=0x0000000000000000) at runtime.m:1213:3
    frame dotnet#4: 0x0000000104544fc8 reloadcontext.iOS`eglib_log_adapter(log_domain=0x0000000000000000, log_level=G_LOG_LEVEL_ERROR, message="* Assertion at ../../../../../mono/mini/interp/interp.c:7176, condition `context' not met\n", user_data=0x0000000000000000) at mono-logger.c:405:2
    frame dotnet#5: 0x000000010456093c reloadcontext.iOS`monoeg_g_logstr(log_domain=0x0000000000000000, log_level=G_LOG_LEVEL_ERROR, msg="* Assertion at ../../../../../mono/mini/interp/interp.c:7176, condition `context' not met\n") at goutput.c:134:2
    frame dotnet#6: 0x0000000104560598 reloadcontext.iOS`monoeg_g_logv_nofree(log_domain=0x0000000000000000, log_level=G_LOG_LEVEL_ERROR, format="* Assertion at %s:%d, condition `%s' not met\n", args="e\x12z\x04\x01") at goutput.c:149:2
    frame dotnet#7: 0x000000010456061c reloadcontext.iOS`monoeg_assertion_message(format="* Assertion at %s:%d, condition `%s' not met\n") at goutput.c:184:22
    frame dotnet#8: 0x0000000104560674 reloadcontext.iOS`mono_assertion_message(file="../../../../../mono/mini/interp/interp.c", line=7176, condition="context") at goutput.c:203:2
    frame dotnet#9: 0x000000010459b570 reloadcontext.iOS`interp_get_resume_state(jit_tls=0x000000014900d000, has_resume_state=0x000000016fc7a9f4, interp_frame=0x000000016fc7a9e8, handler_ip=0x000000016fc7a9e0) at interp.c:7176:2
    frame dotnet#10: 0x0000000104319420 reloadcontext.iOS`compute_frame_info(thread=0x0000000104fe4130, tls=0x0000000149014e00, force_update=1) at debugger-agent.c:3422:3
    frame dotnet#11: 0x0000000104320d40 reloadcontext.iOS`thread_commands(command=1, p="", end="", buf=0x000000016fc7acf8) at debugger-agent.c:9048:3
    frame dotnet#12: 0x000000010431cca0 reloadcontext.iOS`debugger_thread(arg=0x0000000000000000) at debugger-agent.c:10132:10
    frame dotnet#13: 0x000000010447eb04 reloadcontext.iOS`start_wrapper_internal(start_info=0x0000000000000000, stack_ptr=0x000000016fc7b000) at threads.c:1232:3
    frame dotnet#14: 0x000000010447e788 reloadcontext.iOS`start_wrapper(data=0x000000028203ef40) at threads.c:1305:8
    frame dotnet#15: 0x0000000190a11d8c libsystem_pthread.dylib`_pthread_start + 15
[...]
```

Thanks to @drasticactions for helping me to reproduce.

Fixes https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1050615

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src/mono/mono/mini/interp/interp.c

@@ -7186,12 +7186,13 @@ interp_get_resume_state (const MonoJitTlsData *jit_tls, gboolean *has_resume_sta
 {
 	g_assert (jit_tls);
 	ThreadContext *context = (ThreadContext*)jit_tls->interp_context;
-	g_assert (context);
-	*has_resume_state = context->has_resume_state;
-	if (context->has_resume_state) {
-		*interp_frame = context->handler_frame;
-		*handler_ip = (gpointer)context->handler_ip;
-	}
+
+	*has_resume_state = context ? context->has_resume_state : FALSE;
+	if (!*has_resume_state)
+		return;
+
+	*interp_frame = context->handler_frame;
+	*handler_ip = (gpointer)context->handler_ip;
 }
 
 /*