Add missing class var

synapse/rest/media/v1/download_resource.py

@@ -34,7 +34,10 @@ class DownloadResource(Resource):
 
         self.media_repo = media_repo
         self.server_name = hs.hostname
+
+        # Both of these are expected by @request_handler()
         self.clock = hs.get_clock()
+        self.version_string = hs.version_string
 
     def render_GET(self, request):
         self._async_render_GET(request)