Updated Sortable.js to catch empty "order" array

If I don't set up the Store Get function (because I'm only using Set) fully, I get the error "TypeError: order is undefined" at line 1057 of Sortable.js.  (I don't want to change the order of the original list so I don't have a return statement, or return null.)  This fixes that error message.

Sortable.js

@@ -1117,12 +1117,14 @@
 				}
 			}, this);
 
+			if (typeof order !== 'undefined') {
 				order.forEach(function (id) {
 					if (items[id]) {
 						rootEl.removeChild(items[id]);
 						rootEl.appendChild(items[id]);
 					}
 				});
+			}
 		},