Bug 1109540 - Improve GStreamerReader duration handling. r=k17e

dom/media/gstreamer/GStreamerReader.cpp

@@ -70,6 +70,7 @@ GStreamerReader::GStreamerReader(AbstractMediaDecoder* aDecoder)
   mMP3FrameParser(aDecoder->GetResource()->GetLength()),
   mDataOffset(0),
   mUseParserDuration(false),
+  mLastParserDuration(-1),
 #if GST_VERSION_MAJOR >= 1
   mAllocator(nullptr),
   mBufferPool(nullptr),