Merge "DO NOT MERGE - MPEG4Extractor: Check mLastTrack before dereferencing." into klp-dev am: 8caef85235 am: b512f4ab42 am: d18d8fac61  -s ours am: 54c0001dc9  -s ours am: 253e3ae0ba am: 42e8d24ca9  -s ours am: 0bed5b7803 am: 682bb8b4fa am: c8a7c1a69d
am: 6a21e6ca3f  -s ours

Change-Id: I5f1cf35b8419300fbb4fc94fde26cee4b94bc280