Fix NPE reported on users list when HTTP session ends

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1546373 13f79535-47bb-0310-9956-ffa450edef68
Additional fix required for bug 55799

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1546383 13f79535-47bb-0310-9956-ffa450edef68