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: 25ca25a009

Change-Id: If594777dbd569093c6be4dd04f10b39c254b37f5