Merge pull request #3384 from wyklion/patch-1

HighLightLayer removeMesh bug.  _meshes not delete.

src/Layer/babylon.highlightlayer.ts

@@ -824,10 +824,9 @@
                 if (meshHighlight.observerDefault) {
                     mesh.onAfterRenderObservable.remove(meshHighlight.observerDefault);
                 }
+                delete this._meshes[mesh.uniqueId];
             }
 
-            this._meshes[mesh.uniqueId] = null;
-
             this._shouldRender = false;
             for (var meshHighlightToCheck in this._meshes) {
                 if (this._meshes[meshHighlightToCheck]) {
@@ -951,4 +950,4 @@
             this.onSizeChangedObservable.clear();
         }
     }
-} 
+}