Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56446
Clearer handling of exceptions when calling a method on a POJO based WebSocket endpoint. Based on a suggestion by Eugene Chung.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1595898 13f79535-47bb-0310-9956-ffa450edef68