Avoid a crash when reading a SMS and a Subscriber could not be resolved.
It is not clear why the read was failing. The sender_id and the receiver_id
was valid for the given sms. I assume that the database has been locked
due external access to it.
The side-effect is that in case of such a failure the sms_queue will start
to deliver starting from subscriber id = 0 again.
#1 0x0000000000428bec in sms_from_result (net=0x156a270, result=0x15eda30) at db.c:1146
#2 0x000000000042a8e0 in db_sms_get_unsent_by_subscr (net=0x156a270,
min_subscr_id=<optimized out>, failed=<optimized out>) at db.c:1255
#3 0x000000000042e900 in take_next_sms (smsq=<optimized out>) at sms_queue.c:193
#4 sms_submit_pending (_data=0x158e300) at sms_queue.c:227
#5 0x00007f3fd30de3bc in osmo_timers_update () at timer.c:243
#6 0x00007f3fd30de69b in osmo_select_main (polling=0) at select.c:133
#7 0x0000000000406fbc in main (argc=9, argv=<optimized out>) at bsc_hack.c:346
(gdb) frame 1
#1 0x0000000000428bec in sms_from_result (net=0x156a270, result=0x15eda30) at db.c:1146
1146 strncpy(sms->src.addr, sms->sender->extension, sizeof(sms->src.addr)-1);
(gdb) p *sms
(gdb) p sms->sender
$1 = (struct gsm_subscriber *) 0x0
(gdb) p sender_id
$2 = <optimized out>
900394acf3