small fix

app.js

@@ -70,7 +70,9 @@ io.on('connection',  function(socket) {
     socket.on('disconnect', () => {
 		const room = socket.handshake.query.id;
 		console.log('user ' + socket.id + ' disconnected');
-		queue[room]=[];
+		if (typeof queue[room] === "undefined") {
+			queue[room]=[];
+	    }
 		console.log('create queue: ' + room);
     });
 });