Fix ZMQWebSocketHandlers handling their own little FSM instances

lib/tfw/networking/zmq_websocket_handler.py

@@ -44,9 +44,12 @@ class ZMQWebSocketHandler(WebSocketHandler):
 
 
 class FSMManagingSocketHandler(ZMQWebSocketHandler):
+    fsm = None
+
     def __init__(self, FSM, application, request, **kwargs):
         super().__init__(application, request, **kwargs)
-        self.fsm = FSM()
+        if self.fsm is None:
+            FSMManagingSocketHandler.fsm = FSM()
         self.fsm.subscribe_message_handler(self.handle_fsm_message)
 
     def handle_fsm_message(self, message):