Fix bug in mod_usertrack when no CookieName is set.

PR: 24483
Submitted by:	Manni Wood <manniwood planet-save.com>
Reviewed by:	Cliff Woolley, Jim Jagielski


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@102890 13f79535-47bb-0310-9956-ffa450edef68