do redirect the children of the window group
do redirect the children of the window group

thinko fix in MCompositeWindowGroup::updateWindowPixmap()

nemomobile-graveyard/mcompositor,nemomobile-graveyard/mcompositor,nemomobile-graveyard/mcompositor,nemomobile-graveyard/mcompositor,nemomobile-graveyard/mcompositor,nemomobile-graveyard/mcompositor