Caused by a `LoadComponentsAsync()` call being fired from a worker
thread, which will throw exceptions since the recent addition of safety
checks around that method.
Closes#16651.
When a ruleset is not available, the `Find` call would return null. When
a null is passed to the constructor, `BeatmapInfo` would create an "osu"
ruleset, which tries to get stored to realm and fails on duplicate
primary key.
Probably need to add better safeties against this (or change that
constructor...) but this will fix the migration process.
Probably not serious enough to pull the build. This only affects
rulesets like karaoke which have custom beatmaps.
```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()
```