Fix query string handling for proxied URLs.

PR: 14518
Submitted by: michael teitler <michael.teitler cetelem.fr>,
    Jan Kratochvil <rcpt-dev.AT.httpd.apache.org jankratochvil.net>


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@104884 13f79535-47bb-0310-9956-ffa450edef68