Exception on _pong_not_received for websockets

[NotSqrt]

Long story short

Hi!
An exception occurs when closing the websocket connection in _pong_not_received if the connection was already dropped somehow :

  File "aiohttp/web_ws.py", line 88, in _pong_not_received
    self._req.transport.close()
AttributeError: 'NoneType' object has no attribute 'close'

Expected behaviour

No exception.

Actual behaviour

self._req is not None, but self._req.transport is None.

Your environment

Python 3.5, aiohttp==2.0.5, standard loop, server behind nginx.

The issue is happening with really bad websocket clients, not web browsers, that may drop connections without sending close control frames.

Thanks !

[fafhrd91]

should be fixed in master

[lock]

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