Prevent null pointer dereference in setup() if radio is not available.

[rnauber]

Hi,
if your device's radio is not recognized, a nasty null pointer dereference crashes your device. This patch fixes that.

Best,
Richard

--- Miniterm on /dev/ttyUSB0  921600,8,N,1 ---
--- Quit: Ctrl+C | Menu: Ctrl+T | Help: Ctrl+T followed by Ctrl+H ---
??:??:?? 2 ERROR: No UBLOX GPS found
??:??:?? 2 Hoping that NMEA might work
??:??:?? 2 WANT GPS=1
??:??:?? 2 GxGSA NOT available
??:??:?? 2 External Notification Plugin Disabled
??:??:?? 2 NOTE! Recording critical error 6 at src/main.cpp:21f
??:??:?? 2 Starting meshradio init...
??:??:?? 2 (bw=125, sf=12, cr=4/8) packet symLen=32 ms, payloadSize=16, time 2269 ms
??:??:?? 2 Set radio: name=LongSlow, config=3, ch=0, power=0
??:??:?? 2 Radio myRegion->freq: 903.080017
??:??:?? 2 Radio myRegion->spacing: 2.160000
??:??:?? 2 Radio myRegion->numChannels: 13
??:??:?? 2 Radio channel_num: 0
??:??:?? 2 Radio frequency: 903.080017
??:??:?? 2 Short packet time: 2269 msec
??:??:?? 2 Set radio: final power level=17
??:??:?? 2 RF95 init result -2
??:??:?? 2 Current limit set to 100.000000
??:??:?? 2 Current limit set result -16
??:??:?? 2 Warning: Failed to find RF95 radio
??:??:?? 2 Starting meshradio init...
??:??:?? 2 (bw=125, sf=12, cr=4/8) packet symLen=32 ms, payloadSize=16, time 2269 ms
??:??:?? 2 Set radio: name=LongSlow, config=3, ch=0, power=0
??:??:?? 2 Radio myRegion->freq: 903.080017
??:??:?? 2 Radio myRegion->spacing: 2.160000
??:??:?? 2 Radio myRegion->numChannels: 13
??:??:?? 2 Radio channel_num: 0
??:??:?? 2 Radio frequency: 903.080017
??:??:?? 2 Short packet time: 2269 msec
??:??:?? 2 Set radio: final power level=22
??:??:?? 5 SX126x init result -2
??:??:?? 5 Current limit set to 140.000000
??:??:?? 5 Current limit set result -707
??:??:?? 5 Warning: Failed to find SX1262 radio
??:??:?? 5 WiFi ... Forced AP Mode
??:??:?? 5 Waiting for SSL Cert to be generated.
??:??:?? 5 Existing SSL Certificate found!
??:??:?? 5 Retrieved Private Key: 1193 Bytes
??:??:?? 5 Retrieved Certificate: 780 Bytes
??:??:?? 5 SSL Cert Ready!
[D][WiFiGeneric.cpp:374] _eventCallback(): Event: 0 - WIFI_READY
??:??:?? 5 ************ [WiFi-event] event: 0 ************
??:??:?? 5 WiFi interface ready
??:??:?? 5 Starting (Forced) WIFI AP: ssid=meshtasticAdmin, ok=1
[D][WiFiGeneric.cpp:374] _eventCallback(): Event: 14 - AP_START
??:??:?? 5 ************ [WiFi-event] event: 14 ************
??:??:?? 5 WiFi access point started
??:??:?? 5 ... Starting network services
??:??:?? 5 mDNS responder started
??:??:?? 5 mDNS Host: Meshtastic.local
??:??:?? 5 MY IP AP ADDRESS: 192.168.42.1
??:??:?? 5 Starting NTP time client
??:??:?? 5 Initializing Web Server ...
??:??:?? 5 Starting Secure Web Server...
??:??:?? 5 Starting Insecure Web Server...
??:??:?? 5 Web Servers Ready! :-) 
??:??:?? 5 API server listening on TCP port 4403
??:??:?? 5 NOTE! Recording critical error 3 at src/main.cpp:294
Guru Meditation Error: Core  1 panic'ed (LoadProhibited). Exception was unhandled.
Core 1 register dump:
PC      : 0x400e0f8c  PS      : 0x00060430  A0      : 0x800dda89  A1      : 0x3ffd34b0  
A2      : 0x00000000  A3      : 0x000000ed  A4      : 0x00000001  A5      : 0x3ffc9de0  
A6      : 0x447a0000  A7      : 0x3ffbb688  A8      : 0x00060023  A9      : 0x3ffbac7c  
A10     : 0x00000000  A11     : 0x00000000  A12     : 0x80090ca8  A13     : 0x3ffd33e0  
A14     : 0x00000000  A15     : 0x3ffd15c0  SAR     : 0x0000000a  EXCCAUSE: 0x0000001c  
EXCVADDR: 0x00000048  LBEG    : 0x400014fd  LEND    : 0x4000150d  LCOUNT  : 0xfffffffc  

ELF file SHA256: 0000000000000000

Backtrace: 0x400e0f8c:0x3ffd34b0 0x400dda86:0x3ffd3500 0x401213c2:0x3ffd3530
  #0  0x400e0f8c:0x3ffd34b0 in RadioInterface::getPacketTime(unsigned int) at src/mesh/RadioInterface.h:205
  #1  0x400dda86:0x3ffd3500 in setup() at src/main.cpp:667
  #2  0x401213c2:0x3ffd3530 in loopTask(void*) at /home/olg/.platformio/packages/framework-arduinoespressif32/cores/esp32/main.cpp:14

Rebooting...

[mc-hamster]

This is excellent! Thank you! Will merge as soon as the CI completes.