Allow parsing empty RTCP TargetBitrate messages, but stop sending them.

webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc

Index: webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
diff --git a/webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc b/webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
index 583083b6acf2b388d5d75ff6e8b109818fc0b150..d559eefd9d1104c570ac0dd7c3a5ad3e6de85d72 100644
--- a/webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
+++ b/webrtc/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
@@ -204,9 +204,8 @@ void ExtendedReports::ParseVoipMetricBlock(const uint8_t* block,
 
 void ExtendedReports::ParseTargetBitrateBlock(const uint8_t* block,
                                               uint16_t block_length) {
-  target_bitrate_ = rtc::Optional<TargetBitrate>(TargetBitrate());
-  if (!target_bitrate_->Parse(block, block_length))
-    target_bitrate_ = rtc::Optional<TargetBitrate>();
+  target_bitrate_.emplace();
+  target_bitrate_->Parse(block, block_length);
 }
 }  // namespace rtcp
 }  // namespace webrtc