op/clip: ensure that roundRect is always closed

Floating point error may accumulate and the round rect may not
necessarily close up entirely. Add an additional "Close" to ensure
it's properly closed.

Signed-off-by: Egon Elbre <egonelbre@gmail.com>

op/clip/shapes.go

@@ -54,6 +54,7 @@ func (rr RRect) Op(ops *op.Ops) Op {
 	p.Begin(ops)
 	p.Move(rr.Rect.Min)
 	roundRect(&p, rr.Rect.Size(), rr.SE, rr.SW, rr.NW, rr.NE)
+	p.Close()
 
 	return Outline{
 		Path: p.End(),
@@ -84,6 +85,7 @@ func (b Border) Op(ops *op.Ops) Op {
 	p.Begin(ops)
 	p.Move(b.Rect.Min)
 	roundRect(&p, b.Rect.Size(), b.SE, b.SW, b.NW, b.NE)
+	p.Close()
 
 	return Stroke{
 		Path: p.End(),