Server crash when WebSocket is closed in threading mode

[miguelgrinberg]

Discussed in miguelgrinberg/Flask-SocketIO#1958

Traceback (most recent call last):
  File "/home/dev/python/python-engineio/src/engineio/async_drivers/threading.py", line 36, in wait
    return self.ws.receive()
  File "/home/dev/python/flask-socketio/venv/lib/python3.8/site-packages/simple_websocket/ws.py", line 112, in receive
    raise ConnectionClosed(self.close_reason, self.close_message)
simple_websocket.ws.ConnectionClosed: Connection closed: 1005

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/dev/python/flask-socketio/venv/lib/python3.8/site-packages/flask/app.py", line 2548, in __call__
    return self.wsgi_app(environ, start_response)
  File "/home/dev/python/flask-socketio/src/flask_socketio/__init__.py", line 43, in __call__
    return super(_SocketIOMiddleware, self).__call__(environ,
  File "/home/dev/python/python-engineio/src/engineio/middleware.py", line 63, in __call__
    return self.engineio_app.handle_request(environ, start_response)
  File "/home/dev/python/python-socketio/src/socketio/server.py", line 607, in handle_request
    return self.eio.handle_request(environ, start_response)
  File "/home/dev/python/python-engineio/src/engineio/server.py", line 410, in handle_request
    packets = socket.handle_get_request(
  File "/home/dev/python/python-engineio/src/engineio/socket.py", line 103, in handle_get_request
    return getattr(self, '_upgrade_' + transport)(environ,
  File "/home/dev/python/python-engineio/src/engineio/socket.py", line 158, in _upgrade_websocket
    return ws(environ, start_response)
  File "/home/dev/python/python-engineio/src/engineio/async_drivers/threading.py", line 23, in __call__
    return self.app(self)
  File "/home/dev/python/python-engineio/src/engineio/socket.py", line 190, in _websocket_handler
    pkt = websocket_wait()
  File "/home/dev/python/python-engineio/src/engineio/socket.py", line 163, in websocket_wait
    data = ws.wait()
  File "/home/dev/python/python-engineio/src/engineio/async_drivers/threading.py", line 38, in wai
t
    raise IOError()