Avoid iterating in uninitialized result

src/lib/gevent_ws/__init__.py

@@ -262,6 +262,8 @@ class WebSocketHandler(WSGIHandler):
 
     def process_result(self):
         if "wsgi.websocket" in self.environ:
+            if self.result is None:
+                return
             # Flushing result is required for werkzeug compatibility
             for elem in self.result:
                 pass