Fixed bugs in Overflow control.

- Tries to take as much space as possible.
- Draw buffer should be exactly size needed.

ui/overflow.go

@@ -86,6 +86,10 @@ func (o *overflow) Arrange(ctx Context, bounds geom.RectangleF32, offset geom.Po
 	}
 }
 
+func (o *overflow) DesiredSize(ctx Context) geom.PointF32 {
+	return geom.PtF32(geom.NaN32(), geom.NaN32())
+}
+
 func (o *overflow) Handle(ctx Context, e Event) {
 	hor, ver := o.shouldScroll(o.bounds)
 	if hor {
@@ -119,6 +123,7 @@ func (o *overflow) Render(ctx Context) {
 	}
 
 	var content = o.Content.Bounds()
+	content.Min = geom.ZeroPtF32
 	if o.buffer == nil || o.buffer.Width() != content.Dx() || o.buffer.Height() != content.Dy() {
 		if o.buffer != nil {
 			o.buffer.Destroy()