Updates the cached screen rectangles for all ZOrderedViews.
virtual void Z_UpdateCachedRects();
Every CZOrderedView object contains a cached version of its screen rectangle.
These rectangles get invalid, if their parent view (the CZOrderedViewManager) is
moved. This method tests, if the view was moved and updates the cached
retangles of all child views accordingly. This method must always be called,
before the cached rectangles are used.