Wrap _invoke_xblock_handler in a bulk_op.

lms/djangoapps/courseware/module_render.py

@@ -908,6 +908,13 @@ def _invoke_xblock_handler(request, course_id, usage_id, handler, suffix):
     if error_msg:
         return JsonResponse(object={'success': error_msg}, status=413)
 
+    # Make a CourseKey from the course_id, raising a 404 upon parse error.
+    try:
+        course_key = CourseKey.from_string(course_id)
+    except InvalidKeyError:
+        raise Http404
+
+    with modulestore().bulk_operations(course_key):
         instance, tracking_context = get_module_by_usage_id(request, course_id, usage_id)
 
         # Name the transaction so that we can view XBlock handlers separately in