fix clip layer.

Runtime/flow/clip_path_layer.cs

             var clipPathBounds = this._clipPath.getBounds();
             context.cullRect = context.cullRect.intersect(clipPathBounds);
 
+            this.paintBounds = Rect.zero;
             if (!context.cullRect.isEmpty) {
                 var childPaintBounds = Rect.zero;
                 this.prerollChildren(context, matrix, ref childPaintBounds);

Runtime/flow/clip_rect_layer.cs

 
             context.cullRect = context.cullRect.intersect(this._clipRect);
 
+            this.paintBounds = Rect.zero;
             if (!context.cullRect.isEmpty) {
                 var childPaintBounds = Rect.zero;
                 this.prerollChildren(context, matrix, ref childPaintBounds);

Runtime/flow/clip_rrect_layer.cs

             var clipPathBounds = this._clipRRect.outerRect;
             context.cullRect = context.cullRect.intersect(clipPathBounds);
 
+            this.paintBounds = Rect.zero;
             if (!context.cullRect.isEmpty) {
                 var childPaintBounds = Rect.zero;
                 this.prerollChildren(context, matrix, ref childPaintBounds);