core: follow up to r1708084.

We don't want to process the subrequest either in ap_sub_req_method_uri()
if the quick-handler returned an error (or any final status).


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1708095 13f79535-47bb-0310-9956-ffa450edef68