fix toggle no work due an window.opener.document access denied

Prevent for continue to interpret javascript if stopping with
Error: Permission denied to access property "document"
Maybe rule browser "Same-origin policy" or unexisting object.

On course sidebar, toggle unwork & print "toggle" in place of +
for simply see this (js) error, go to login.php ;-)

this function is called in jscript/ATutor_js.php on line 381
ATutor.users.preferences.setStyles()

jscripts/ATutor.js

@@ -579,7 +579,7 @@ ATutor.users.preferences = ATutor.users.preferences || {};
 
         jQuery('#pref_style').replaceWith(pref_style);
         if (window.opener) {
-            jQuery('#pref_style', window.opener.document).replaceWith(pref_style);
+            try {jQuery('#pref_style', window.opener.document).replaceWith(pref_style);}catch(err){}finally{}
         }
     };