Fix thos issue

elements/core/core.go

@@ -113,6 +113,7 @@ func (control CoreControl) HasImage () (has bool) {
 // DamageRegion pushes the selected region of pixels to the parent element. This
 // does not need to be called when responding to a resize event.
 func (control CoreControl) DamageRegion (bounds image.Rectangle) {
+	if control.core.canvas == nil { return }
 	if control.core.onDamage != nil {
 		control.core.onDamage(canvas.Cut(control.core.canvas, bounds))
 	}

elements/fun/clock.go

@@ -61,7 +61,7 @@ func (element *AnalogClock) draw () {
 	state := theme.PatternState { }
 	pattern := element.theme.Pattern(theme.PatternSunken, state)
 	inset   := element.theme.Inset(theme.PatternSunken)
-	artist.FillRectangle(element, pattern, bounds)
+	artist.FillRectangle(element.core, pattern, bounds)
 
 	bounds = inset.Apply(bounds)
 
@@ -107,6 +107,5 @@ func (element *AnalogClock) radialLine (
 	max := element.Bounds().Min.Add(image.Pt (
 		int(math.Cos(radian) * outer * width + width),
 		int(math.Sin(radian) * outer * height + height)))
-	// println(min.String(), max.String())
-	artist.Line(element, source, 1, min, max)
+	artist.Line(element.core, source, 1, min, max)
 }