Fix an edge case where AllocateSpaceForPayload causes OTA to fail am: 51e08b90a7 am: fc006c787b

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1596613

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: Ie38011073e9078b0057b2819fc740755467b98d8