Fix javascript error when calling "Save as event" from email message view page

plugins/calendar/calendar_base.js

@@ -78,6 +78,7 @@ function rcube_calendar(settings)
     {
       if (event.title) {
         this.ui.add_event(event);
+        if (rcmail.message_list)
           rcmail.message_list.blur();
       }
     };