Ensures that packets_lost is always positive.

This is a quick fix to ensure that we don't wrap the value.  A proper
solution would be to ensure that the packets_lost field is signed and
handled as signed at all places it's used.

Bug: webrtc:9598
Change-Id: I3622f2a61aa3af57db6292ef4c0a8e97c4833aa4
Reviewed-on: https://webrtc-review.googlesource.com/92881
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Reviewed-by: Magnus Flodman <mflodman@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24212}

video/report_block_stats.cc

@@ -10,6 +10,8 @@
 
 #include "video/report_block_stats.h"
 
+#include <algorithm>
+
 namespace webrtc {
 
 namespace {
@@ -33,7 +35,8 @@ void ReportBlockStats::Store(const RtcpStatistics& rtcp_stats,
                              uint32_t remote_ssrc,
                              uint32_t source_ssrc) {
   RTCPReportBlock block;
-  block.packets_lost = rtcp_stats.packets_lost;
+  // TODO(srte): Remove this clamp when packets_lost is made signed.
+  block.packets_lost = std::max(0, rtcp_stats.packets_lost);
   block.fraction_lost = rtcp_stats.fraction_lost;
   block.extended_highest_sequence_number =
       rtcp_stats.extended_highest_sequence_number;