bug 1139874 check for shutdown before asking the reader for buffered r=bholley

--HG--
extra : rebase_source : cbc7f06a89dfbaf22eb590c51ba709a4757296d0

dom/media/MediaDecoder.cpp

@@ -1609,7 +1609,7 @@ void MediaDecoder::Invalidate()
 // Constructs the time ranges representing what segments of the media
 // are buffered and playable.
 nsresult MediaDecoder::GetBuffered(dom::TimeRanges* aBuffered) {
-  NS_ENSURE_TRUE(mDecoderStateMachine, NS_ERROR_FAILURE);
+  NS_ENSURE_TRUE(mDecoderStateMachine && !mShuttingDown, NS_ERROR_FAILURE);
   return mDecoderStateMachine->GetBuffered(aBuffered);
 }