Assertion in SIP transaction module init when restarting pjsua (thanks Roni Salfati for the report)

[nanang]

The assertion line:

Assertion failed: mod_tsx_layer.endpt==((void *)0),
file pjsip\src\pjsip\sip_transaction.c, line 436

Or if the test peer has the SIP session timer enabled:

Assertion failed: is_initialized,
file pjsip\src\pjsip-ua\sip_timer.c, line 609

This assertion doesn't always happen, however it is reproducible with a special test app containing a loop of: pjsua create+init+start, register, making call, call hold/unhold, call hangup, pjsua destroy. Supplying non-zero flag to the pjsua_destroy2() will lead to the assertion faster.