code: Send userlist before adding new registered user to avoid duplicate.

code/hub.go

@@ -78,10 +78,9 @@ func handleIncomingMessage(sender *websocket.Conn, msg string) {
 			sender.WriteJSON(newError("You have an illegal nickname"))
 			return
 		}
+		sendUserList(sender)
 
 		usernames[sender] = username
-
-		sendUserList(sender)
 		m := newMessage("server", username+" has joined the chat")
 		m.dispatch()
 		return