Username validation in installer

[KevinSupertramp]

Hello,

I think there's no username validation in the installer because I could use my email address as username but it's said in the documentation that only alphanumeric characters, numbers, dot and underscore are allowed.

I checked in the source but couldn't find anything about it. I'm hope I'm not wrong !

Best regards

[floriandotpy]

Fixed via 7d06acf