Canvas2D: patch child order

src/Canvas2d/babylon.prim2dBase.ts

@@ -2259,8 +2259,8 @@
         private addChild(child: Prim2DBase) {
             child._parent = this;
             this._boundingBoxDirty();
-            this._patchHierarchyDepth(child);
             this._children.push(child);
+            this._patchHierarchyDepth(child);
         }
 
         /**
@@ -2629,7 +2629,7 @@
 
         private _patchHierarchyDepth(child: Prim2DBase) {
             child._hierarchyDepth = this._hierarchyDepth + 1;
-            child._hierarchyDepthOffset = this._hierarchyDepthOffset + ((this._children.length + 1) * this._siblingDepthOffset);
+            child._hierarchyDepthOffset = this._hierarchyDepthOffset + ((this._children.indexOf(child) + 1) * this._siblingDepthOffset);
             child._siblingDepthOffset = this._siblingDepthOffset / Canvas2D.hierarchyLevelMaxSiblingCount;           
         }