SDP failed to be created which lead to crash caused by rejected HOLD request

[riza]

Scenario:

1. Terminal C receives intial INVITE (incoming call) from server without SDP
2. Terminal C sends 200 OK with SDP
3. Terminal C receives ACK with SDP
4. SDP negotiation succeeds, call is connected
5. Terminal C sends INVITE (Hold) to server
6. Server rejects hold request with 488 (server spec). Provisional media was cleared
7. Terminal C receives INVITE (media update for "transfer") from server without SDP. Because provisional media was cleared, error was returned when creating SDP (PJ_EAFNOTSUP).
8. Terminal C sends 200 OK with SDP
9. Terminal C receives ACK with SDP. Because there's no provisional media, Error was raised when updating media.

This ticket will check if the provisional media was cleared (7) and if so, will
reinitialize media channel.

Thanks to Marcus Froeschl for the report