Merge r1523235 from trunk:

mod_cache: Avoid a crash with strcmp() when the hostname is not provided.

Submitted by: minfrin
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1524167 13f79535-47bb-0310-9956-ffa450edef68