Fix `MultiplayerPlayer` never calling `Reset` on `GameplayClockContainer`

This call is responsible for ensuring the clock is in a stopped state.

osu.Game/Screens/OnlinePlay/Multiplayer/MultiplayerPlayer.cs

@@ -148,6 +148,9 @@ protected override void StartGameplay()
                 loadingDisplay.Show();
                 client.ChangeState(MultiplayerUserState.ReadyForGameplay);
             }
+
+            // This will pause the clock, pending the gameplay started callback from the server.
+            GameplayClockContainer.Reset();
         }
 
         private void failAndBail(string message = null)