edge: fix issue with disposing a non-existing transceiver
edge: fix issue with disposing a non-existing transceiver

fixes an issue where, when SRD was called, an attempt was made
to dispose the icetransport of a transceiver which was not created.

Acidburn0zzz/adapter,webrtc/adapter,Acidburn0zzz/adapter,xdumaine/adapter,Acidburn0zzz/adapter,xdumaine/adapter,webrtc/adapter