-Assign brushTarget GridLayout only if it exists (#304)

Author: ChuanXin-Unity

Editor/Brushes/GameObjectBrush/GameObjectBrush.cs

@@ -349,7 +349,11 @@ private void GetGrid(ref GridLayout gridLayout, ref GameObject brushTarget)
             if (brushTarget == hiddenGrid)
                 brushTarget = null;
             if (brushTarget != null)
-                gridLayout = brushTarget.GetComponent<GridLayout>();
+            {
+                var targetGridLayout = brushTarget.GetComponent<GridLayout>();
+                if (targetGridLayout != null)
+                    gridLayout = targetGridLayout;
+            }
         }
 
         /// <summary>Clears all data of the brush.</summary>