fix image slice bug

Runtime/ui/renderer/cmdbufferCanvas/rendering/canvas_impl.cs

 
         void _clipRect(Rect rect) {
             var path = uiPath.create();
-            path.addRect(uiRectHelper.fromRect(rect));
+            path.addRect(uiRectHelper.fromRect(rect).Value);
             this._clipPath(path);
             uiPathCacheManager.putToCache(path);
         }
                         break;
                     case DrawSaveLayer cmd: {
                         saveCount++;
-                        this._saveLayer(uiRectHelper.fromRect(cmd.rect), uiPaint.fromPaint(cmd.paint));
+                        this._saveLayer(uiRectHelper.fromRect(cmd.rect).Value, uiPaint.fromPaint(cmd.paint));
                         break;
                     }
 
                     }
 
                     case DrawImageRect cmd: {
-                        this._drawImageRect(cmd.image, uiRectHelper.fromRect(cmd.src), uiRectHelper.fromRect(cmd.dst),
+                        this._drawImageRect(cmd.image, uiRectHelper.fromRect(cmd.src), uiRectHelper.fromRect(cmd.dst).Value,
                             uiPaint.fromPaint(cmd.paint));
                         break;
                     }
-                            uiRectHelper.fromRect(cmd.center), uiRectHelper.fromRect(cmd.dst),
+                            uiRectHelper.fromRect(cmd.center).Value, uiRectHelper.fromRect(cmd.dst).Value,
                             uiPaint.fromPaint(cmd.paint));
                         break;
                     }
             matrix.preTranslate(offset.dx, offset.dy);
 
             var mesh = TextBlobMesh.create(textBlob.Value, scale, matrix);
-            var textBlobBounds = matrix.mapRect(uiRectHelper.fromRect(textBlob.Value.boundsInText));
+            var textBlobBounds = matrix.mapRect(uiRectHelper.fromRect(textBlob.Value.boundsInText).Value);
 
             // request font texture so text mesh could be generated correctly
             var style = textBlob.Value.style;

Runtime/ui/renderer/common/geometry/rect.cs

     }
 
     public static class uiRectHelper {
-        public static uiRect fromRect(Rect rect) {
+        public static uiRect? fromRect(Rect rect) {
+            if (rect == null) {
+                return null;
+            }
             return new uiRect(rect.left, rect.top, rect.right, rect.bottom);
         }
 

Runtime/ui/renderer/common/picture.cs

                 case uiDrawClipRRect cmd: {
                     var state = this._getState();
 
-                    var rect = state.xform.mapRect(uiRectHelper.fromRect(cmd.rrect.outerRect));
+                    var rect = state.xform.mapRect(uiRectHelper.fromRect(cmd.rrect.outerRect).Value);
                     state.scissor = state.scissor == null ? rect : state.scissor.Value.intersect(rect);
                     this._setState(state);
                     break;
                 }
                 case uiDrawPicture cmd: {
                     var state = this._getState();
-                    var rect = state.xform.mapRect(uiRectHelper.fromRect(cmd.picture.paintBounds));
+                    var rect = state.xform.mapRect(uiRectHelper.fromRect(cmd.picture.paintBounds).Value);
                     this._addPaintBounds(rect);
                     break;
                 }
                     var rect = uiRectHelper.fromRect(
-                        cmd.textBlob.Value.shiftedBoundsInText(cmd.offset.Value.dx, cmd.offset.Value.dy));
+                        cmd.textBlob.Value.shiftedBoundsInText(cmd.offset.Value.dx, cmd.offset.Value.dy)).Value;
                     rect = state.xform.mapRect(rect);
 
                     var paint = cmd.paint;