[box-layout] Don't shrink when adjustments are set
[box-layout] Don't shrink when adjustments are set

If a BoxLayout has adjustments, it is intended that it should scroll, so
layout as if it has gotten its preferred size.

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