uix:Settings fix handeling of numeric input

Weird how it went unnoticed.

To reproduce the Issue this Fixes..

1. Open settings, edit a numeric setting like fps.

The value isn't updated and the next time you try setting the value, it crashes.

Need to test further::
-  are there situations that rely on the self.value being numeric?
- should the conversion be moved to where the Textinput's text is being set?