update_engine: update another read size am: 6963a9296d

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3234524

Change-Id: I4f4a7e03a05e3de029c713f350cca204acaa8b78
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>