When performing a fast transition to another OPEN network the RSN
element won't be there and therefore the bss->rsne is gonna be NULL.
Fix crash by not accessing the rsne member when performing a fast
transition to an AP that doe snot advertise any RSN IE.
Crash caught with gdb:
src/station.c:station_transition_start() 186, target 34:8f:27:2f:b8:fc
Program received signal SIGSEGV, Segmentation fault.
handshake_state_set_authenticator_ie (s=0x555555626eb0, ie=0x0) at src/handshake.c:163
163 s->authenticator_ie = l_memdup(ie, ie[1] + 2u);
(gdb) bt
#0 handshake_state_set_authenticator_ie (s=0x555555626eb0, ie=0x0) at src/handshake.c:163
#1 0x0000555555561a98 in fast_transition (netdev=0x55555562fbe0, target_bss=0x55555561f4a0,
over_air=over_air@entry=true, cb=0x55555556d5b0 <station_fast_transition_cb>) at src/netdev.c:3164
#2 0x0000555555565dfd in netdev_fast_transition (netdev=<optimized out>, target_bss=<optimized out>,
cb=<optimized out>) at src/netdev.c:3232
#3 0x000055555556ccbd in station_transition_start (bss=0x55555561f4a0, station=0x555555617da0)
at src/station.c:1261
#4 station_roam_scan_notify (err=<optimized out>, bss_list=<optimized out>, userdata=0x555555617da0)
at src/station.c:1444
#5 0x0000555555579560 in scan_finished (sc=0x55555562bf80, err=err@entry=0, bss_list=0x55555561bd90,
sr=0x555555626b30, wiphy=<optimized out>) at src/scan.c:1234
#6 0x0000555555579620 in get_scan_done (user=0x555555618920) at src/scan.c:1264
#7 0x00005555555abd23 in destroy_request (data=0x55555561b000) at ell/genl.c:673
#8 0x00005555555ac129 in process_unicast (nlmsg=0x7fffffffc310, genl=0x55555560b7a0) at ell/genl.c:940
#9 received_data (io=<optimized out>, user_data=0x55555560b7a0) at ell/genl.c:1039
#10 0x00005555555a8aa3 in io_callback (fd=<optimized out>, events=1, user_data=0x55555560b840)
at ell/io.c:126
#11 0x00005555555a7ccd in l_main_iterate (timeout=<optimized out>) at ell/main.c:473
#12 0x00005555555a7d9c in l_main_run () at ell/main.c:520
#13 l_main_run () at ell/main.c:502
#14 0x00005555555a7fac in l_main_run_with_signal (callback=<optimized out>, user_data=0x0)
at ell/main.c:642
#15 0x000055555555e5b8 in main (argc=<optimized out>, argv=<optimized out>) at src/main.c:519
8106d82b4e