Bug 1183518. Part 3 - early bailout from MediaDecoder::NotifyBytesConsumed when shutting down. r=jya.

dom/media/MediaDecoder.cpp

@@ -976,12 +976,12 @@ void MediaDecoder::NotifyPrincipalChanged()
 void MediaDecoder::NotifyBytesConsumed(int64_t aBytes, int64_t aOffset)
 {
   MOZ_ASSERT(NS_IsMainThread());
-  MOZ_ASSERT(mDecoderStateMachine);
 
   if (mShuttingDown || mIgnoreProgressData) {
     return;
   }
 
+  MOZ_ASSERT(mDecoderStateMachine);
   ReentrantMonitorAutoEnter mon(GetReentrantMonitor());
   if (aOffset >= mDecoderPosition) {
     mPlaybackStatistics->AddBytes(aBytes);