Fix crash when all acks in a feedback message arrive too late.

webrtc/modules/congestion_controller/send_side_congestion_controller.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 222 matching lines @@
   transport_feedback_adapter_.AddPacket(ssrc, sequence_number, length,
                                         pacing_info);
 }
 
 void SendSideCongestionController::OnTransportFeedback(
     const rtcp::TransportFeedback& feedback) {
   RTC_DCHECK(worker_thread_checker_.CalledOnValidThread());
   transport_feedback_adapter_.OnTransportFeedback(feedback);
   std::vector<PacketFeedback> feedback_vector =
       transport_feedback_adapter_.GetTransportFeedbackVector();
-  if (feedback_vector.empty())
-    return;
   DelayBasedBwe::Result result;
   {
     rtc::CritScope cs(&bwe_lock_);
     result = delay_based_bwe_->IncomingPacketFeedbackVector(feedback_vector);
   }
   if (result.updated)
     bitrate_controller_->OnDelayBasedBweResult(result);
 }
 
 std::vector<PacketFeedback>
@@ skipping 54 matching lines @@
 bool SendSideCongestionController::IsSendQueueFull() const {
   return pacer_->ExpectedQueueTimeMs() > PacedSender::kMaxQueueLengthMs;
 }
 
 bool SendSideCongestionController::IsNetworkDown() const {
   rtc::CritScope cs(&network_state_lock_);
   return network_state_ == kNetworkDown;
 }
 
 }  // namespace webrtc