The users theme choice gets reset

[Marius786]

When an administrator edits a user from the backend, the users theme choice gets reset to the first option in the dropdown.

Use case:

1. Create user1, and install the plugin;
2. Login as the user1 and select some theme as theme per user option;
   2.1. Missing step: Logout as user1 and login again as user1 then logout again;
3. Then login as the admin, and change the users name/address. Save and logout..
4. Then login as the user1 again, and see the theme has changed.