Merge r1632740 from trunk:

mod_cache: avoid unlikely access to freed memory.
Submitted by: ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1638070 13f79535-47bb-0310-9956-ffa450edef68