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

Change-Id: I74873bdd367f238277c74fec12edf7275ee14435