Segmentation fault when taking device for a walk

[Richard Acayan <mailingradian@gmail.com>]

Hi,

A segmentation fault occurs in station_start_roam() when the station is
disconnected from an access point, or in other words, when the station's
connected_bss is NULL. Usually, this is triggered by a timeout, possibly
scheduled in response to a weak signal event.

This is occurring on my Pixel 3a running postmarketOS/Alpine Linux, when
receding from an access point, on iwd 2.19. I have collected 6 coredumps
of the crash in the span of around 2 weeks and would be willing to use
GDB if more information is necessary for a patch.

Sample:

	Program terminated with signal SIGSEGV, Segmentation fault.
	#0  0x0000aaaadf2086a0 in station_start_roam (station=0xffff8776ae50) at src/station.c:2880
	
	warning: 2880	src/station.c: No such file or directory
	(gdb) bt
	#0  0x0000aaaadf2086a0 in station_start_roam (station=0xffff8776ae50) at src/station.c:2880
	#1  0x0000aaaadf28c544 in timeout_callback (fd=<optimized out>, events=<optimized out>, 
	    user_data=0xffff876b2e20) at ell/timeout.c:68
	#2  timeout_callback (fd=<optimized out>, events=<optimized out>, user_data=0xffff876b2e20)
	    at ell/timeout.c:57
	#3  0x0000aaaadf28b9d0 in l_main_iterate (timeout=<optimized out>) at ell/main.c:461
	#4  0x0000aaaadf28bac0 in l_main_run () at ell/main.c:508
	#5  l_main_run () at ell/main.c:490
	#6  0x0000aaaadf28bce4 in l_main_run_with_signal (
	    callback=callback@entry=0xaaaadf1f1110 <signal_handler>, user_data=user_data@entry=0x0)
	    at ell/main.c:630
	#7  0x0000aaaadf1f0b0c in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:611
	(gdb) p station->connected_bss 
	$1 = (struct scan_bss *) 0x0