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 am: 0b8c6e6a92
am: fc3a6e178b

Change-Id: Ifec682686319d50506e29c99ca9f223f7f704051