Fix "Update Patch" for generic Differential revisions.
You can now help a coworker to update their patch, from the web.
So, if you visit Diff 111 (not yours) and you click "Update Diff", and you paste a valid diff,
you arrive here:
https://we.phorge.it/differential/diff/222/?revisionID=111
That page as default was suggesting some Diffs that are yours. Plus, now it shows Diff 111.
Omitting the Diff from which the workflow was started made no sense and it's certainly an oversight.
Any follow-up change is welcome to modernize the selector using AphrontFormTokenizerControl.
Closes T15538