message: Fix updating degradation preference in SetRtpParameters.
  Degradation preference could be changed before video send stream
  is configured which would cause a crash.
  Cr-Commit-Position: refs/heads/master@{#30141}
diff: @@ -2068,8 +2068,10 @@ webrtc::RTCError WebRtcVideoChannel::WebRtcVideoSendStream::SetRtpParameters(
  UpdateSendState();
  }
  if (new_degradation_preference) {
  + if (source_ && stream_) {
  stream_->SetSource(this, GetDegradationPreference());
  }
  + }
  return webrtc::RTCError::OK();
  }
  