[BUG] /api/v1/users.register registering even when error happens

[cardoso]

{
    "error" : "matheus.cardoso@ is not a valid username, use only letters, numbers, dots, hyphens and underscores [username-invalid]",
    "errorType" : "username-invalid",
    "success" : false
}

#8475 might be a related issue.

Both issues are pretty bad, because they still create the user in our database which takes up the email.

[rafaelks]

@cardoso We'll change the way it works on the apps: if we receive this error, the app will open another screen that will allow the user to see the suggested username and set a new one. There's no easy way to handle this error in our back-end right now.

• API to have suggestion of username ([NEW] REST API to suggest a new username to the user #10640);
• API to set an username (https://rocket.chat/docs/developer-guides/rest-api/users/update/);