If we are doing a fast_redirect, and we don't have a main request, then

make sure that we don't have the sub_req_output_filter.  This was
causing problems when there were multiple sub_Requests, and some should
have had the filter, but the last one shouldn't.

This fixes the final known bug in 2.0.35


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@94470 13f79535-47bb-0310-9956-ffa450edef68