Load draw:corner-radius correctly

Thr draw:corner-radius can be bigger then the actual shape is wide or high. In that case
make the radius half the width/height.

This fixes the problem that the shape in bug 260226 is shown as big as it should.

The actual problem described in the bug report had already be fixed.

BUG: 260226
Reviewed by: boemann
(cherry picked from commit 0502a9d5)