I can't find a better way to do this. It's very hard to trigger an
actual failure in the import process these days. For now I've just made
this work with the new assumptions. May be worth removing the test in
the future if this ever backfires.
Not only does this combine the check into one location, but it also adds
a check on the global `WorkingBeatmap` being updated, which is the only
way I can see the following failure happening:
```csharp
05:19:07 osu.Game.Tests: osu.Game.Tests.Visual.Editing.TestSceneEditorBeatmapCreation.TestAddAudioTrack
05:19:07 Failed TestAddAudioTrack [161 ms]
05:19:07 Error Message:
05:19:07 TearDown : System.NullReferenceException : Object reference not set to an instance of an object.
05:19:07 Stack Trace:
05:19:07 --TearDown
05:19:07 at osu.Game.Database.ModelManager`1.<>c__DisplayClass7_0.<AddFile>b__0(TModel managed) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Database\ModelManager.cs:line 36
05:19:07 at osu.Game.Database.ModelManager`1.<>c__DisplayClass8_0.<performFileOperation>b__0(Realm realm) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Database\ModelManager.cs:line 49
05:19:07 at osu.Game.Database.RealmExtensions.Write(Realm realm, Action`1 function) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Database\RealmExtensions.cs:line 14
05:19:07 at osu.Game.Database.ModelManager`1.performFileOperation(TModel item, Action`1 operation) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Database\ModelManager.cs:line 46
05:19:07 at osu.Game.Database.ModelManager`1.AddFile(TModel item, Stream contents, String filename) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Database\ModelManager.cs:line 36
05:19:07 at osu.Game.Screens.Edit.Setup.ResourcesSection.ChangeAudioTrack(FileInfo source) in C:\BuildAgent\work\ecd860037212ac52\osu.Game\Screens\Edit\Setup\ResourcesSection.cs:line 115
05:19:07 at osu.Game.Tests.Visual.Editing.TestSceneEditorBeatmapCreation.<TestAddAudioTrack>b__13_0() in C:\BuildAgent\work\ecd860037212ac52\osu.Game.Tests\Visual\Editing\TestSceneEditorBeatmapCreation.cs:line 101
05:19:07 at osu.Framework.Testing.Drawables.Steps.AssertButton.checkAssert()
05:19:07 at osu.Framework.Testing.Drawables.Steps.StepButton.PerformStep(Boolean userTriggered)
05:19:07 at osu.Framework.Testing.TestScene.runNextStep(Action onCompletion, Action`1 onError, Func`2 stopCondition)
```
Resolves an issue I've been able to locally reproduce on windows.
Basically, the `File.Copy` would begin while realm was blocking. The
"restore" operation is posted to the `SynchronizationContext` to run on
next update call, but in the mean time the copy would begin, causing a
conflict of interest.
Very dangerous. Only really noticeable on windows.
