message: Check for valid transport before setting criteria.
  Cr-Commit-Position: refs/heads/main@{#35981}
diff: @@ -496,6 +496,12 @@ bool BaseChannel::RegisterRtpDemuxerSink_w() {
  bool ret = network_thread_->Invoke<bool>(
  RTC_FROM_HERE, [this, demuxer_criteria = demuxer_criteria_] {
  RTC_DCHECK_RUN_ON(network_thread());
  + if (!rtp_transport_) {
  + // Transport was disconnected before attempting to update the
  + // criteria. This can happen while setting the remote description.
  + // See chromium:1295469 for an example.
  + return false;
  + }
  // Note that RegisterRtpDemuxerSink first unregisters the sink if
  // already registered. So this will change the state of the class
  // whether the call succeeds or not.
  