Merge pull request #1308 from RaananW/worldcanvas-renderGroup-fix

Making sure parent exists before providing its rendergroup.

src/Canvas2d/babylon.group2d.ts

@@ -803,7 +803,7 @@
 
             if (!rd._cacheNode) {
                 // Check if we have to allocate a rendering zone in the global cache texture
-                var res = this.owner._allocateGroupCache(this, this.parent.renderGroup, curWidth ? new Size(curWidth, curHeight) : null, rd._useMipMap, rd._anisotropicLevel);
+                var res = this.owner._allocateGroupCache(this, this.parent && this.parent.renderGroup, curWidth ? new Size(curWidth, curHeight) : null, rd._useMipMap, rd._anisotropicLevel);
                 rd._cacheNode = res.node;
                 rd._cacheTexture = res.texture;
                 rd._cacheRenderSprite = res.sprite;