* Do not set filter context brigade to NULL (and thus need to recreate it each

  time) but empty it (via APR_BRIGADE_PREPEND) and reuse it. 

Submitted by: Stefan Fritsch <sf sfritsch.de>
Reviewed by: rpluem


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@603227 13f79535-47bb-0310-9956-ffa450edef68