Fix a bug in total_data_length am: 4decfcd3b6

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2208896

Change-Id: I3a760f4154bbd51e23a1539d36dcee94a71f502c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>