Fix a mutex problem in mod_ssl session cache support which

could lead to an infinite loop.

PR:                     12705
Diagnosis submitted by: amund.elstad@ergo.no (Amund Elstad)
Coded by:               Jeff Trawick


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@97048 13f79535-47bb-0310-9956-ffa450edef68