Fix issues after storyboard resource lookup refactor

[bdach]

• Closes Crash on entering some beatmaps #24862

Two regressions from #24809:

Fix StoryboardResourceLookupStore dying on failure to unmap path

Before the introduction of StoryboardResourceLookupStore, missing files would softly fail by use of null fallbacks:

osu/osu.Game/Storyboards/Storyboard.cs

Lines 116 to 119 in 4a7d7c6

	if (!string.IsNullOrEmpty(resolvedPath))
	return textureStore.Get(resolvedPath);
	return null;

After the aforementioned class was added, however, the fallbacks would not work anymore if for whatever reason GetStoragePathFromStoryboardPath() failed to unmap the storyboard asset name to a storage path.

While that helped unearth the other regression (more about that in a second) by making it more loud, it's probably not something we want around due to reliability reasons.

Fix DrawableStoryboardVideo attempting to unmap path once too much

The StoryboardResourceLookupStore cached at storyboard level is supposed to already be handling that; no need for local logic anymore.

This is a baffling oversight on my part since the OP of the original PR mentioned the weird DrawableStoryboardVideo logic explicitly, but then I failed to spot that the PR was nto touching that class at all. Or test storyboards with videos. (I did test storyboards, but only ones without videos.........)

[bdach]

The null!s here are slightly annoying. You would probably very wisely say to do this:

diff --git a/osu.Game/Storyboards/Drawables/DrawableStoryboard.cs b/osu.Game/Storyboards/Drawables/DrawableStoryboard.cs
index c2a58d46ef..631475cce8 100644
--- a/osu.Game/Storyboards/Drawables/DrawableStoryboard.cs
+++ b/osu.Game/Storyboards/Drawables/DrawableStoryboard.cs
@@ -128,7 +128,7 @@ private void updateLayerVisibility()
                 layer.Enabled = passing ? layer.Layer.VisibleWhenPassing : layer.Layer.VisibleWhenFailing;
         }
 
-        private class StoryboardResourceLookupStore : IResourceStore<byte[]>
+        private class StoryboardResourceLookupStore : IResourceStore<byte[]?>
         {
             private readonly IResourceStore<byte[]> realmFileStore;
             private readonly Storyboard storyboard;
@@ -142,21 +142,21 @@ public StoryboardResourceLookupStore(Storyboard storyboard, RealmAccess realm, G
             public void Dispose() =>
                 realmFileStore.Dispose();
 
-            public byte[] Get(string name)
+            public byte[]? Get(string name)
             {
                 string? storagePath = storyboard.GetStoragePathFromStoryboardPath(name);
 
                 return string.IsNullOrEmpty(storagePath)
-                    ? null!
+                    ? null
                     : realmFileStore.Get(storagePath);
             }
 
-            public Task<byte[]> GetAsync(string name, CancellationToken cancellationToken = new CancellationToken())
+            public Task<byte[]?> GetAsync(string name, CancellationToken cancellationToken = new CancellationToken())
             {
                 string? storagePath = storyboard.GetStoragePathFromStoryboardPath(name);
 
                 return string.IsNullOrEmpty(storagePath)
-                    ? Task.FromResult<byte[]>(null!)
+                    ? Task.FromResult<byte[]?>(null)
                     : realmFileStore.GetAsync(storagePath, cancellationToken);
             }
 

But the fun part is that at that point, there is a .NET library NRT fail:

and to make it shut up, you have to do this abomination:

Yes you're reading that right, that's two shut-up operator occurrences. So I decided I'd rather leave well alone.

[peppy]

Yeah. I've tried multiple times to fix nullability in resource stores but it needs to basically happen everywhere at once.

[peppy]

This was a rebase conflict resolution failure 😞