Error Message When Changing Username

How it was found

Hello,

Description:

I have found a bug in your fix other my other report, #243609. I reported this in a new report as this is an error in the error message.

When changing your username that starts with a . the error message is: Username may only contain letters, numbers or the following characters: @ . + - _

A normal user would be confused as it does not state any reason for the . not being allowed at the beginning of their username.

POC:

1. Change your username to a name that starts with a ..
2. You will receive an error message that does not explain why this is not excepted.

Mitigation:

I recommend you add a specific error message that states that your username cannot start with a ..

Thanks!