fix: Correct server connection check in JoinInviteListener to handle initial connections

Author: twisti-dev

surf-clan-velocity/src/main/kotlin/dev/slne/clan/velocity/listener/JoinInviteListener.kt

@@ -25,7 +25,7 @@ object JoinInviteListener {
 
     @Subscribe
     fun onServerConnected(event: ServerConnectedEvent) {
-        if (event.previousServer.isEmpty) return
+        if (event.previousServer.isPresent) return
 
         plugin.container.launch {
             delay(1.seconds)