muilibrary: allow again for groups in page mode not to flicker when redrawing
Firstly, with this code there does not seem to be any problem with
colorwheel in coloradjust as tested via Zune/test, Color tab.
The change itself allows for groups in page mode not to clear the
ares where children are. Previous this was working only for non-page
mode areas and for page mode was causing flicker, because super draw
method (Area) was making a clear on complete object UI space.
git-svn-id: https://svn.aros.org/svn/aros/trunk/AROS@51087 fb15a70f-31f2-0310-bbcc-cdcc74a49acc