Merge "DO NOT MERGE - MPEG4Extractor: Check mLastTrack before dereferencing." into lmp-dev am: b6ba3d7e47  -s ours am: 37e3ea354a am: ea136eb981  -s ours am: 2456e12801 am: fe97b39795 am: 3c76391550 am: 1099791bd6  -s ours am: 0e4feca95e am: 21269e19f5 am: 1d9ec790db
am: 5ad6e5fde7

Change-Id: I1e80b06e01b620e12a3eaaed5911939b0d0ee7e3