fix class cast exception on MailEventServerListener

2016-12-19 08:58:20,777 ERROR [cached4] [atlassian.confluence.event.ConfluenceEventDispatcher] run There was an exception thrown trying to dispatch event [com.atlassian.confluence.cluster.hazelcast.HazelcastClusterEventWrapper[source=null]] from the invoker [com.atlassian.confluence.event.ConfluenceListenerHandlersConfiguration$TimingListenerHandler$1$1@50dd2b40]
 -- event: com.atlassian.confluence.event.events.admin.MailServerEditEvent[source=null] | originatingMemberUuid: c5e0aa3a-c46f-42ea-998b-ca7d2b8f9873
java.lang.ClassCastException: com.atlassian.confluence.cluster.hazelcast.HazelcastClusterEventWrapper cannot be cast to com.atlassian.confluence.event.events.admin.MailServerEditEvent
  at com.atlassian.confluence.event.listeners.MailServerEventListener.handleEvent(MailServerEventListener.java:34)
  at com.atlassian.event.legacy.LegacyListenerHandler$LegacyListenerInvoker.invoke(LegacyListenerHandler.java:55)
  at com.atlassian.confluence.event.ConfluenceListenerHandlersConfiguration$TimingListenerHandler$1$1.invoke(ConfluenceListenerHandlersConfiguration.java:69)
  at com.atlassian.confluence.event.ConfluenceEventDispatcher$VCacheRequestContextRunnableFactory$1.lambda$run$0(ConfluenceEventDispatcher.java:93)
  at com.atlassian.confluence.vcache.VCacheRequestContextOperations.lambda$doInRequestContext$0(VCacheRequestContextOperations.java:50)
  at com.atlassian.confluence.impl.vcache.VCacheRequestContextManager.doInRequestContextInternal(VCacheRequestContextManager.java:87)
  at com.atlassian.confluence.impl.vcache.VCacheRequestContextManager.doInRequestContext(VCacheRequestContextManager.java:71)

Event underlyingEvent = EventUtils.extractWrappedEventOrOriginal(event);

        if (underlyingEvent instanceof MailServerCreateEvent) {
            MailServerCreateEvent createEvent = (MailServerCreateEvent) underlyingEvent;
            MailServer server = createEvent.getServer();
            JmxUtil.registerBean(makeNameForServer(server.getName()), createEvent.getServer());
        } else if (underlyingEvent instanceof MailServerDeleteEvent) {
            JmxUtil.unregisterBean(makeNameForServer(((MailServerDeleteEvent) underlyingEvent).getServer().getName()));
        } else if (underlyingEvent instanceof MailServerEditEvent) {
            //Additionally handle edit events
            MailServerEditEvent editEvent = (MailServerEditEvent) event;
            JmxUtil.unregisterBean(makeNameForServer(editEvent.getOriginalServerName()));
            JmxUtil.registerBean(makeNameForServer(editEvent.getServer().getName()), editEvent.getServer());
        }