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

Change-Id: If2db282f155963e46adcff5fcc05bfc8eba5d59a