Dean Herbert b87d1a61a8 Fix ButtonSystem null reference crash due to missing null check in delayed animations
```csharp
[runtime] 2022-01-27 07:36:34 [error]: System.NullReferenceException: Object reference not set to an instance of an object.
[runtime] 2022-01-27 07:36:34 [error]: at osu.Game.Screens.Menu.ButtonSystem.<>c__DisplayClass56_0.<updateLogoState>b__1() in /Users/dean/Projects/osu/osu.Game/Screens/Menu/ButtonSystem.cs:line 357
[runtime] 2022-01-27 07:36:34 [error]: at osu.Framework.Threading.ScheduledDelegate.RunTaskInternal()
[runtime] 2022-01-27 07:36:34 [error]: at osu.Framework.Threading.Scheduler.Update()
[runtime] 2022-01-27 07:36:34 [error]: at osu.Framework.Graphics.Drawable.UpdateSubTree()
```
2022-01-27 16:39:38 +09:00
..
2021-04-20 17:30:40 +09:00
2019-04-08 15:24:09 +09:00
2021-07-05 23:52:39 +08:00