Assertion when TURN session is deallocated prematurely (thanks Tony Jago Million for the report)

[bennylp]

TURN session may get deallocated prematurely for several reasons, for example if iPhone application is suspended in the background and unable to refresh the allocation in timely manner.

Sample 1 of the assertion:

pjnath/turn_sock.c:433:
PJ_ASSERT_RETURN(turn_sock && addr && addr_len, PJ_EINVAL);

Stack trace:
0   libsystem_kernel.dylib        	0x3558fa1c __pthread_kill + 8
1   libsystem_c.dylib             	0x356663b4 pthread_kill + 52
2   libsystem_c.dylib             	0x3565ebf8 abort + 72
3   libsystem_c.dylib             	0x3568c6d4 __assert_rtn + 140
4   bababoo                       	0x001aeefc pj_turn_sock_sendto + 44
5   bababoo                       	0x001a5cce pj_ice_strans_sendto + 194
6   bababoo                       	0x0019ba34 transport_send_rtp + 72
7   bababoo                       	0x0019d398 transport_send_rtp + 120

Sample 2:

pjnath/turn_sock.c:622:
pj_assert(!"We should shutdown gracefully");

Stack trace:
#0  0x358cda1c in __pthread_kill ()
#1  0x359a43ba in pthread_kill ()
#2  0x3599cbfe in abort ()
#3  0x359ca6da in __assert_rtn ()
#4  0x001af292 in turn_on_send_pkt ()
#5  0x001ad70c in stun_on_send_msg ()
#6  0x001ab702 in stun_tsx_on_send_msg ()
#7  0x001acdb0 in tsx_transmit_msg ()
#8  0x001acfc2 in pj_stun_client_tsx_send_msg ()
#9  0x001aba40 in pj_stun_session_send_msg ()
#10 0x001adfd0 in pj_turn_session_set_perm ()
#11 0x001aed72 in pj_turn_session_sendto ()
#12 0x001aef36 in pj_turn_sock_sendto ()
#13 0x001a5cf4 in pj_ice_strans_sendto ()
#14 0x0019ba5a in transport_send_rtp ()

[bennylp]

(In [3596]) Fixed #1316: Assertion when TURN session is deallocated prematurely (thanks Tony Jago Million for the report)