Fix playing users not being updated on room join

osu.Game/Online/Multiplayer/StatefulMultiplayerClient.cs

@@ -144,6 +144,8 @@ namespace osu.Game.Online.Multiplayer
                     Room = joinedRoom;
                     apiRoom = room;
                     defaultPlaylistItemId = apiRoom.Playlist.FirstOrDefault()?.ID ?? 0;
+                    foreach (var user in joinedRoom.Users)
+                        updateUserPlayingState(user.UserID, user.State);
                 }, cancellationSource.Token).ConfigureAwait(false);
 
                 // Update room settings.