window: Make sure resize grip is above child
window: Make sure resize grip is above child

Make sure the window's resize grip is always above the child. Also add
checks before using the resize-grip in all cases, as it's possible for
the user to remove it from the container.

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