1. Ignore edit list where the sequence doesn't contain a sync
sample, rather than failing.
2. Make Mp4Extractor.readAtomPayload so it doesn't try and read
the same payload twice if a failure occurs parsing it.
3. Make processAtomEnded so that it doesn't pop the moov if
parsing it fails.
Issue: #3351
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=172106244
