Timing out HTTP2 connections logs a traceback

[twm]

Pretty ugly:

<6>[twisted.web.http.HTTPChannel] Timing out client: IPv4Address(type='TCP', host='127.0.0.1', port=39206)
<6>[twisted.web.http.HTTPChannel] Forcibly timing out client: IPv4Address(type='TCP', host='127.0.0.1', port=39206)
<2>[-] Unhandled Error
<2>  Traceback (most recent call last):
<2>    File "/home/twm/yarrharr/yarrharr/scripts/yarrharr.py", line 44, in main
<2>      run()
<2>    File "/home/twm/yarrharr/yarrharr/application.py", line 505, in run
<2>      reactor.run()
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/internet/base.py", line 1261, in run
<2>      self.mainLoop()
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/internet/base.py", line 1270, in mainLoop
<2>      self.runUntilCurrent()
<2>  --- <exception caught here> ---
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/internet/base.py", line 896, in runUntilCurrent
<2>      call.func(*call.args, **call.kw)
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/web/http.py", line 2333, in forceAbortClient
<2>      self.transport.abortConnection()
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/protocols/tls.py", line 435, in abortConnection
<2>      self._shutdownTLS()
<2>    File "/home/twm/yarrharr/.tox/run/lib/python3.5/site-packages/twisted/protocols/tls.py", line 338, in _shutdownTLS
<2>      shutdownSuccess = self._tlsConnection.shutdown()
<2>  builtins.AttributeError: 'NoneType' object has no attribute 'shutdown'
<2>  

Yes, even a bonus newline.

This is https://twistedmatrix.com/trac/ticket/9462

[twm]

Now twisted/twisted#9462