Fixes small bugs

+ With MDNLinks and bonfireExecute being run on step challenges.
+ Return when common isn't loaded in reBindModals instead of throwing.

client/main.js

@@ -252,7 +252,7 @@ $(document).ready(function() {
 
   function reBindModals() {
     if (!window.common) {
-      throw new Error('common framework should be loaded.');
+      return;
     }
     var common = window.common;