[automerger] Check NAL size before looking inside am: e0c020969d am: 8c4ae8057c am: 767a82a9d6 am: f7d9bba9b1 am: e04b7c8c06 am: 25e199f787 am: 93962ef505 am: 714148f6eb

Change-Id: Id6c6d3bab191bb1f1aa12aa77e5ba8a136ad28ae