mod_proxy_http: Core dumped under high load. PR 50335

trunk patch: http://svn.apache.org/viewvc?view=revision&revision=1534321
             http://svn.apache.org/viewvc?view=revision&revision=1550061

Submitted by: Jan Kaluza <jkaluza redhat.com>
Reviewed by: jim, jorton, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1553540 13f79535-47bb-0310-9956-ffa450edef68