Writes to file, same name, same subgraph, do not conflict

Accidental ECL in testing 13264 demonstrates that a Thor Workunit will write to the same filename from two "Disk Write" components in the same subgraph without complaint, even if OVERWRITE option not provided.

FYI, the file names were static.

Granted, this was accidental and I wouldn't expect real-world to encounter this much, but still curious.