Merge "libsnapshot: Stop reading ops once we reach a footer." am: a1a5fdc6ee am: 2e831f7e66 am: e1435f5463

Original change: https://android-review.googlesource.com/c/platform/system/core/+/1475324

Change-Id: Ic0e4cc939d298cbd33c9bf95a87fa31c0288f19d