International domain names not handled in Additional email addresses of Create User secreen

Hello team, Nothing urgent nor major but issue for IDNs: International domain names are not handled in Additional email addresses of the Create User secreen.

Inputting same IDN as the one on which the user is created (or that another one that is created separately) is not allowed as IDN.

To reproduce:

1. create domain tést.com (works)
2. create user me (@tést.com) with alias him@tést.com
3. Save to create user
4. See error "Failed to save user : The additional email domain 'tést.com' is not managed by Virtualmin" (This is Bug 1)
5. Go back and put the expanded IDN him@xn--.....
6. Save to create user: Works!
7. See that the main username for IMAP/POP has IDN for its username (me), but not the IDN but instead has the expanded IDN in it. (minor bug 2). The login should imho be international (if it works).