Fix a bug in total_data_length am: 4decfcd3b6 am: 53af28b8d4

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

Change-Id: I4c32edbe5e16ab6c431792342cde29d3c0f0c24f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/scripts/update_payload/payload.py b/scripts/update_payload/payload.py
index c63e5d1..cc15753 100644
--- a/scripts/update_payload/payload.py
+++ b/scripts/update_payload/payload.py
@@ -166,7 +166,7 @@
     # us total data length
     for partition in reversed(self.manifest.partitions):
       for op in reversed(partition.operations):
-        if op.data_offset > 0:
+        if op.data_length > 0:
           return op.data_offset + op.data_length
     return 0