On PJSUA2, application will not be notified when when SDP nego fails due to unsupported codec.

[riza]

Ticket #1916 enables on_incoming_call() called from on_create_media_transport() for PJSUA2.

However, after the on_incoming_call() invocation, there is a chance that the call is disconnected by the library (e.g: due to unsupported codec or unsupported SIP capability requirement). Unfortunately, there is a bug in the library that application will not be informed about the call disconnection in such scenario.

The patch will add check for codec and capability support from the SDP before
calling on_incoming_call(). In this case, when the check fails then on_incoming_call() will not be called.

However, actually there is still a chance of failure in further step of call verification, so the call may get rejected by the library after incoming call callback is invoked. In this case, call state callback on_call_state() will be invoked to notify application about call disconnection.

Thanks to Ryan Wallach for the report.

[riza]

In r5928:

Close #2173: On PJSUA2, application will not be notified when when SDP nego fails due to unsupported codec.

[ming]

In 5930:

Re #2173: Fixed assertion caused by PJMEDIA_SDP_EMISSINGCONN, if incoming INVITE contains unsupported media (such as video when PJSIP is built without video).

The assertion happens in:
pjsip_inv_verify_request3: Assertion `(status=pjmedia_sdp_validate(l_sdp))==PJ_SUCCESS' failed.