Merge "DO NOT MERGE - MPEG4Extractor: Check mLastTrack before dereferencing." into lmp-mr1-dev am: 622fd04e88 am: 862b281476  -s ours am: 5e94f64995 am: d7ec581644 am: 60d1b58bf1
am: bb08cac420  -s ours

Change-Id: Iec20a874f4502a040119674de4ff98919dfff1a7