Prevent autocomplete space following username at login

[Kufat]

No popup because this usually happens for reasons that aren't the user's fault.

[brunnre8]

Thank you for the PR.
I don't think this is the right approach though, we should just switch the user input field to the normal v-model and let vue do it with the .trim modifier on it.
I've already PRed the rewrite #4753 so all that you need to do is add the trim modifier onto it.