Bug 1374774: P4. Correct H264 telemetry reporting. r=gerald

The code couldn't have worked, mNeedSPSForTelemetry can only be set if we didn't get an H264 extradata in the MP4 metadata.
So any calls to HasSPS(sample->mExtraData) would have always returned false.

MozReview-Commit-ID: 3PcRXJHBJyC

--HG--
extra : rebase_source : 4137b9c985ffe7ee3958fad509149bf911229eed

dom/media/fmp4/MP4Demuxer.cpp

@@ -520,10 +520,14 @@ MP4TrackDemuxer::GetSamples(int32_t aNumSamples)
   }
   for (const auto& sample : samples->mSamples) {
     // Collect telemetry from h264 Annex B SPS.
-    if (mNeedSPSForTelemetry && mp4_demuxer::H264::HasSPS(sample->mExtraData)) {
+    if (mNeedSPSForTelemetry) {
       RefPtr<MediaByteBuffer> extradata =
         mp4_demuxer::H264::ExtractExtraData(sample);
-      mNeedSPSForTelemetry = AccumulateSPSTelemetry(extradata);
+      if (mp4_demuxer::H264::HasSPS(extradata)) {
+        RefPtr<MediaByteBuffer> extradata =
+          mp4_demuxer::H264::ExtractExtraData(sample);
+        mNeedSPSForTelemetry = AccumulateSPSTelemetry(extradata);
+      }
     }
   }