update_engine: fix checkpointing am: 37f212d9fe am: 858d0a8b4a

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3218418

Change-Id: Ie0754bb933ffa5a732ec40e62a387683b18abe10
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>