* Do not even sent an empty brigade down the filter chain if the headers

  have not been sent by the AJP server so far. Even an empty brigade
  will trigger the headers filter to create the (in this case incomplete)
  HTTP headers of the response.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1153531 13f79535-47bb-0310-9956-ffa450edef68