Fixed a bug where legacy instructor dash's email editor failed to load

lms/templates/courseware/instructor_dashboard.html

@@ -546,11 +546,13 @@ function goto( mode)
       <input type="submit" name="action" value="Send email">
     </div>
     <script type="text/javascript">
+    $(document).ready(function(){
       var emailEditor = XBlock.initializeBlock($('.xblock-studio_view'));
       document.idashform.onsubmit = function() {
         this.message.value = emailEditor.save()['data'];
         return true;
       }
+    });
     </script>
 
     <p>These email actions run in the background, and status for active email tasks will appear in a table below.