PR53420: Proxy responses with error status and
"ProxyErrorOverride On" hang until proxy timeout.

Regression from 2.2. It was introduced by r912063
in order to fix PR41646.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1615289 13f79535-47bb-0310-9956-ffa450edef68