QPID-6025: Java port of QpidConfig give NPE when listing queue/exchanges, added code to agentdata Queue and Exchange to return empty Map to be consistent with C++ Broker and also for good measure added some defensive code to QpidConfig.java

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1619161 13f79535-47bb-0310-9956-ffa450edef68