Don't crash logger when transport is None

[mpaolini]

When websocket client closes connection I often get this (on the server)

[...]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/marco/src/aiohttp/aiohttp/helpers.py", line 389, in log
    [message, environ, response, transport, time]))
  File "/home/marco/src/aiohttp/aiohttp/helpers.py", line 376, in _format_line
    return tuple(m(args) for m in self._methods)
  File "/home/marco/src/aiohttp/aiohttp/helpers.py", line 376, in <genexpr>
    return tuple(m(args) for m in self._methods)
  File "/home/marco/src/aiohttp/aiohttp/helpers.py", line 333, in _format_a
    return args[3].get_extra_info('peername')[0]
AttributeError: 'NoneType' object has no attribute 'get_extra_info'

Could not cook a test, let me know if you need it

[asvetlov]

I can live without a test for this particular case.

[asvetlov]

Thanks

[lock]

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