Renameuser does not properly sanitize/canonicalize old username in rename form.

It is possible to provide a string that is an invalid username that can be canonicalized to a valid one (e.g. "Test user" with two spaces), which will trigger a "The user does not exist." error even if the account "Test user" does exist.

(There is a separate process of uppercasing the first letter of the provided username; the RenameUserWarning hook can receive the lowercase username before it is adjusted. This might be a separate bug too.)

Version: unspecified
Severity: normal
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=60241