Don't attempt to kill a stale entry that cannot be revalidated so early

in the process, as this will happen later anyway as necessary. We may want
to serve the stale entry should the backend not be available.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1023398 13f79535-47bb-0310-9956-ffa450edef68