Don't invalidate ContainerBox's children when something is set

redundantly

box.go

@@ -117,6 +117,7 @@ func (this *box) SetColor (c color.Color) {
 }
 
 func (this *box) SetTexture (texture canvas.Texture) {
+	if this.texture == texture { return }
 	this.texture = xcanvas.AssertTexture(texture)
 	this.invalidateDraw()
 }

containerbox.go

@@ -31,11 +31,13 @@ func (backend *Backend) NewContainerBox() tomo.ContainerBox {
 }
 
 func (this *containerBox) SetColor (c color.Color) {
+	if this.color == c { return }
 	this.box.SetColor(c)
 	this.invalidateTransparentChildren()
 }
 
 func (this *containerBox) SetTexture (texture canvas.Texture) {
+	if this.texture == texture { return }
 	this.box.SetTexture(texture)
 	this.invalidateTransparentChildren()
 }