Removed checking `undefined` against receiveShadow

`receiveShadow` is always boolean. skip redundant check `object.receiveShadow !== undefined &&`.

editor/js/Sidebar.Object.js

@@ -539,7 +539,7 @@ function SidebarObject( editor ) {
 
 			}
 
-			if ( object.receiveShadow !== undefined && object.receiveShadow !== objectReceiveShadow.getValue() ) {
+			if ( object.receiveShadow !== objectReceiveShadow.getValue() ) {
 
 				if ( object.material !== undefined ) object.material.needsUpdate = true;
 				editor.execute( new SetValueCommand( editor, object, 'receiveShadow', objectReceiveShadow.getValue() ) );