Fix rollback detection am: 1bcd7d700c

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2439694

Change-Id: I88a95c15fb76ff9862550022d93380ccd4e61f8a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>