[codegen] Fix breakage due to diff between internal and external protobuf APIs.
[codegen] Fix breakage due to diff between internal and external protobuf APIs.

But fundamentally we were taking GetFlag() on something that wasn't a flag.

PiperOrigin-RevId: 477827508

google/xls,google/xls,google/xls,google/xls,google/xls,google/xls