title: 'NoneType' object has no attribute '_app_data' in scrapy\twisted\openssl
body: <p>During the scraping process using scrapy one error appears in my logs from time to time.
  It doesnt seem to be anywhere in my code, and looks like it something inside twisted\openssl.
  Any ideas what caused this and how to get rid of it?</p>
  
  <p>Stacktrace here:</p>
  
  <pre><code>[Launcher,27487/stderr] Error during info_callback
      Traceback (most recent call last):
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/twisted/protocols/tls.py", line 415, in dataReceived
          self._write(bytes)
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/twisted/protocols/tls.py", line 554, in _write
          sent = self._tlsConnection.send(toSend)
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/OpenSSL/SSL.py", line 1270, in send
          result = _lib.SSL_write(self._ssl, buf, len(buf))
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/OpenSSL/SSL.py", line 926, in wrapper
          callback(Connection._reverse_mapping[ssl], where, return_code)
      --- &lt;exception caught here&gt; ---
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/twisted/internet/_sslverify.py", line 1055, in infoCallback
          return wrapped(connection, where, ret)
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/twisted/internet/_sslverify.py", line 1157, in _identityVerifyingInfoCallback
          transport = connection.get_app_data()
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/OpenSSL/SSL.py", line 1589, in get_app_data
          return self._app_data
        File "/opt/webapps/link_crawler/lib/python2.7/site-packages/OpenSSL/SSL.py", line 1148, in __getattr__
          return getattr(self._socket, name)
      exceptions.AttributeError: 'NoneType' object has no attribute '_app_data'
  </code></pre>