Merge r1560977 from trunk:

mod_session: When we have a session we were unable to decode, behave as if there was no session at all.

Submitted by: minfrin
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1560991 13f79535-47bb-0310-9956-ffa450edef68