Assertion when sending SUBSCRIBE failed synchronously

[nanangizz]

Reported that assertion happens with this call stack trace:

Crashed: Thread: SIGABRT  0x0000000000000000
#00 pc 0x51894 libc.so (BuildId: 058e3ec96fa600fb840a6a6956c6b64e)
#01 pc 0x51864 libc.so (BuildId: 058e3ec96fa600fb840a6a6956c6b64e)
#02 pc 0x51c64 libc.so (BuildId: 058e3ec96fa600fb840a6a6956c6b64e)
#03 pc 0x661c08 libpjsua2.so (pjsip_dlg_dec_lock) (BuildId: 4922aaff88b25fc51d5455bb4471a2161724c7f0)
#04 pc 0x5ea78c libpjsua2.so (subscribe_buddy_presence) (BuildId: 4922aaff88b25fc51d5455bb4471a2161724c7f0)
#05 pc 0x5ea0b8 libpjsua2.so (pjsua_buddy_update_pres) (BuildId: 4922aaff88b25fc51d5455bb4471a2161724c7f0)

After investigating the provided log file, the problem seems to be accessing buddy states after getting reset/null-ed. Check subscribe_buddy() code here:

pjproject/pjsip/src/pjsua-lib/pjsua_pres.c

Lines 2142 to 2149 in 2d5e351

	if (presence) {
	status = pjsip_pres_send_request(buddy->sub, tdata);
	} else {
	status = pjsip_dlg_event_send_request(buddy->sub, tdata);
	}
	if (status != PJ_SUCCESS) {
	pjsip_dlg_dec_lock(buddy->dlg);
	pjsip_pres_terminate(buddy->sub, PJ_FALSE);

When the sending fails synchronously, the callbacks of transaction and event subscription may be invoked. From the callbacks, the event subscription terminates the subscription and PJSUA presence resets the buddy states. So when the send operation returns, the buddy states (e.g: buddy->dlg & buddy->sub) may have been set to NULL and pjsip_dlg_dec_lock(NULL) will raise an assertion.

[sauwming]

this doesn't seem to be used?