Fix the defpath memory leak ASan keeps complaining about

Currently, running ksh under ASan without the ASAN_OPTIONS variable
set to 'detect_leaks=0' usually ends with ASan complaining about
a memory leak in defpathinit() (this leak doesn't grow in a loop, so
no regression test was added to leaks.sh). Reproducer:
   $ ENV=/dev/null arch/*/bin/ksh
   $ cp -?
   cp: invalid option -- '?'
   Try 'cp --help' for more information.
   $ exit

   =================================================================
   ==225132==ERROR: LeakSanitizer: detected memory leaks

   Direct leak of 85 byte(s) in 1 object(s) allocated from:
       #0 0x7f6dab42d459 in __interceptor_calloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
       ksh93#1 0x5647b77fe144 in sh_calloc /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/init.c:265
       ksh93#2 0x5647b788fea9 in path_addcomp /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/path.c:1567
       ksh93#3 0x5647b78911ed in path_addpath /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/path.c:1705
       ksh93#4 0x5647b7888e82 in defpathinit /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/path.c:442
       ksh93#5 0x5647b78869f3 in ondefpath /home/johno/GitRepos/KornShell/ksh/src/cmd/ksh93/sh/path.c:67
   --- cut ---
   SUMMARY: AddressSanitizer: 174 byte(s) leaked in 2 allocation(s).

src/cmd/ksh93/sh/path.c:
- Move the code for allocating defpath from defpathinit() into its
  own dedicated function called std_path(). This function is called
  by defpathinit() and onstdpath() to obtain the current string stored
  in the defpath variable. This bugfix is adapted from a fork of
  ksh2020:
  l0stman/ksh@db5c83a

NEWS

@@ -9,6 +9,9 @@ Any uppercase BUG_* names are modernish shell bug IDs.
   shell when suspending (Ctrl+Z) an external command invoked by a dot script
   or POSIX shell function, or via 'eval'.
 
+- Fixed a memory leak that occurred when running a command that was found on
+  the PATH.
+
 2022-01-26:
 
 - On Cygwin, ksh now executes scripts that do not have a #! path itself,

src/cmd/ksh93/sh/path.c

@@ -58,14 +58,21 @@ static int		checkdotpaths(Pathcomp_t*,Pathcomp_t*,Pathcomp_t*,int);
 static void		checkdup(register Pathcomp_t*);
 static Pathcomp_t	*defpathinit(void);
 
-static const char	*defpath;	/* default path that finds standard utilities */
+static const char *std_path(void)
+{
+	static const char *defpath;		/* default path that finds standard utilities */
+	if(!defpath)
+	{
+		if(!(defpath = astconf("PATH",NIL(char*),NIL(char*))))
+			abort();
+		defpath = sh_strdup(defpath);   /* the value returned by astconf() is short-lived */
+	}
+	return(defpath);
+}
 
 static int ondefpath(const char *name)
 {
-	const char *cp;
-	if(!defpath)
-		defpathinit();
-	cp = defpath;
+	const char *cp = std_path();
 	if(cp)
 	{
 		const char *sp;
@@ -433,13 +440,7 @@ Pathcomp_t *path_nextcomp(register Pathcomp_t *pp, const char *name, Pathcomp_t
 
 static Pathcomp_t* defpathinit(void)
 {
-	if(!defpath)
-	{
-		if(!(defpath = astconf("PATH",NIL(char*),NIL(char*))))
-			abort();
-		defpath = sh_strdup(defpath);	/* the value returned by astconf() is short-lived */
-	}
-	return(path_addpath((Pathcomp_t*)0,(defpath),PATH_PATH));
+	return(path_addpath((Pathcomp_t*)0,std_path(),PATH_PATH));
 }
 
 static void pathinit(void)