[ScrollBar] Fix reactive prop not actually working
[ScrollBar] Fix reactive prop not actually working

If you set a scroll-bar reactive or unreactive, it would always remain
reactive. Also, a scroll-bar would default be unreactive, even though
it's reactive and acts as such. Both fixed.

pwithnall/mx,clutter-project/mx,pwithnall/mx,jonnylamb/mx,clutter-project/mx,pwithnall/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,jonnylamb/mx,jonnylamb/mx,pwithnall/mx