[Lock/Login screen themes] Don't send empty password
When hitting the enter key on an empty password field, an empty string will be sent, which is always wrong. This is annoying when you wake up your computer using the enter key and it immediately tries to log in with the wrong password.
Instead, don't do anything when hitting the enter key if the password field is empty.
Question: is an empty string ever a valid password such that this could lock users out of their systems? Because we wouldn't want to do that. :)