gl renderer: Ignore rounded clip that only increase the clip

gl renderer: Ignore rounded clip that only increase the clip

This fixes the widget factory rendering too much.

In the widget-factory, we generally have a pretty small update area (two
spinners and a progressbar). We take the extents of that as a update
area and inital clip.

However, the first clip node we see is from the toplevel window, which
essentially increases the clip again to almost the entire window.

Fix that by ignoring such cases.