[BUGFIX] Clear link/node in sidebar destory

lib/infobox/main.js

@@ -10,7 +10,7 @@ define(['infobox/link', 'infobox/node', 'infobox/location'], function (Link, Nod
     function destroy() {
       if (el && el.parentNode) {
         el.parentNode.removeChild(el);
-        el = undefined;
+        node = link = el = undefined;
         sidebar.reveal();
       }
     }