1680: add sanitation of error-message from codeharbor

Author: kkoehn

app/assets/javascripts/exercises.js

@@ -389,7 +389,7 @@ $(document).on('turbolinks:load', function () {
             url: Routes.export_external_confirm_exercise_path(exerciseID),
             dataType: 'json',
             success: function (response) {
-                $messageDiv.html(response.message)
+                $messageDiv.html(_.escape(response.message))
                 $actionsDiv.html(response.actions);
 
                 if (response.status === 'success') {