Fix download progress offset error am: 5440fe3cfe

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2870744

Change-Id: Ic280840563065e10f864e4ecc48bb0b2142e9e03
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>