Skip FEC reads for partial updates am: 212b053645

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3356640

Change-Id: Idc4be8f6f3235f0f773e0d45f1749c066b6c37a9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>