[m-rev.] diff: don't add already done modules to a work queue

[Zoltan Somogyi]

This should not need review.

Zoltan.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Log.ds
Type: application/octet-stream
Size: 446 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230909/b5168fe6/attachment.obj>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: DIFF.ds
Type: application/octet-stream
Size: 15332 bytes
Desc: not available
URL: <http://lists.mercurylang.org/archives/reviews/attachments/20230909/b5168fe6/attachment-0001.obj>