Fix so that errordocument works when a error gets returned from the

proxy.
Problem was ErrorHandler thought it was in some kind of recursion and
couldn't find the custom error document
Obtained from: Jin Hong <jinh@cnet.com>
Submitted by:
Reviewed by:   Ian Holsman


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91757 13f79535-47bb-0310-9956-ffa450edef68