Avoid possible NPE when no charset is specified

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1552805 13f79535-47bb-0310-9956-ffa450edef68
Add missing tag

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1552806 13f79535-47bb-0310-9956-ffa450edef68