DO NOT MERGE - MPEG4Extractor: Check mLastTrack before dereferencing. am: 0338b14e28  -s ours am: 648b682eeb am: d558903f8c  -s ours am: ad1141b06b am: fbe82fe0fa am: 7e8c500e2c am: 5eea83feb7  -s ours am: 6e39a8cb87 am: 701bc80a92 am: 02ea93dc37
am: e8c14297ac

Change-Id: I76368c79a7a6181a2ec7dbd07707e3cf1254554d