방이 하나도 없을 때 안내 메세지 추가

@@ -28,7 +28,12 @@ const Rooms: React.FC = () => {
     });
   }, []);
 
-  useEffect(refreshRooms, []);
+  useEffect(() => {
+    // 뒤로가기 키로 빠져나오면 ping listener를 unsubscribe
+    socket.off('ping');
+
+    refreshRooms();
+  }, []);
 
   return (
     <Main>
@@ -37,7 +42,11 @@ const Rooms: React.FC = () => {
         <Create />
       </div>
       <div className='mt-auto w-screen flex flex-col items-center'>
-        {rooms.map((room) => (<RoomBlock key={room.uuid} room={room} />))}
+        {
+          rooms.length > 0 ?
+          rooms.map((room) => (<RoomBlock key={room.uuid} room={room} />))
+          : (<div className='text-lg'>There's no room at all.</div>)
+        }
       </div>
     </Main>
   )