Assertions triggered by lock codec after unsuccessful SDP negotiation or media update failure

[nanang]

Known cases:

• SDP negotiation done unsuccessfully, e.g: no common codec, so no local/remote active SDP resulted:

  Assertion failed: (neg->active_local_sdp), function pjmedia_sdp_neg_get_active_local, file ../src/pjmedia/sdp_neg.c, line 188.
  

• SDP negotiation done successfully, but then media update fails and the media may get deactivated (port set to 0 and attributes removed):

  Assertion failed: (!"SDP should have been validated!"), function is_non_av_fmt, file ../src/pjsua-lib/pjsua_call.c, line 3047.
  

[nanang]

(In [3374]) Fix #1163:

• Fixed lock codec to always be done after successful media update, and pend the lock codec until call state CONFIRMED if media update is done in call state EARLY but remote does not support UPDATE method.
• Added additional checks in lock_codec() and perform_lock_codec(), e.g: skip locking codec when media deactivated.