SDP failed to be created when creating an offer if provisional media has been cleared

[riza]

When a re-INVITE/UPDATE fails, pjsua will clear its provisional medias. This may cause assertion when creating subsequent SDP offers.

Example scenario:

1. Normal call is established between caller and callee.
2. Caller sends INVITE (Hold) to callee.
3. Callee rejects hold request with 488. Provisional media was cleared.
4. Caller creates another offer (either because it receives an INVITE without SDP, or if it's trying to repeat step 2 above by calling pjsua_call_set_hold()). Because provisional media has been cleared, error was returned when creating SDP (PJ_EAFNOTSUP).

This ticket will check if the provisional media was cleared and if so, will reinitialize media channel.

Thanks to Marcus Froeschl for the report

[riza]

In 5082:

Re #1848: Fix failed to create SDP which lead to crash caused by rejected HOLD request.

[ming]

In 5094:

Fixed #1848: SDP failed to be created when provisional media has been cleared