Fix multiple tests via null checks and changing ToLive to Detach

flow

osu.Game/Beatmaps/BeatmapManager.cs

@@ -200,6 +200,7 @@ namespace osu.Game.Beatmaps
         /// <param name="query">The query.</param>
         /// <returns>The first result for the provided query, or null if no results were found.</returns>
         public BeatmapInfo? QueryBeatmap(Expression<Func<BeatmapInfo, bool>> query) => beatmapModelManager.QueryBeatmap(query)?.Detach();
+        // TODO: move detach to usages?
 
         /// <summary>
         /// Saves an <see cref="IBeatmap"/> file against a given <see cref="BeatmapInfo"/>.