ICL websocket does not send close frame at shutdown

[w-samuelgauthier]

Steps to reproduce:

1. Start icl.exe

2. Run code below:

   from websockets.exceptions import ConnectionClosedError, ConnectionClosedOK
   from websockets.sync.client import connect
   
   websocket = connect(uri='ws://localhost:25010')
   try:
       websocket.send('{"command":"icl_shutdown"}')
       for message in websocket:
           print(message)
   except ConnectionClosedOK as e:
       print(f'Connection normally closed: {e}')
   except ConnectionClosedError as e:
       print(f'Protocol error or network failure: {e}')

3. Output: Protocol error or network failure: no close frame received or sent