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

Change-Id: Iad8f148c9adf0304e711a26ba68ba5085b57e313