Fix bug in mod_usertrack when no CookieName is set.

PR: 24483
Submitted by:	Manni Wood <manniwood planet-save.com>
Reviewed by:	Cliff Woolley, Justin Erenkrantz, Sander Striker


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@102892 13f79535-47bb-0310-9956-ffa450edef68