Shortcut common case of single score to avoid individual check overheads

Author: peppy

osu.Server.Queues.ScoreStatisticsProcessor/Commands/Maintenance/MarkNonPreservedScoresCommand.cs

@@ -158,7 +158,15 @@ private static bool checkIsUserHigh(IEnumerable<SoloScore> userScores, SoloScore
 
             Debug.Assert(scores.Any());
 
-            preservedAlternatives = new HashSet<SoloScore>();
+            // shortcut for case of single score match
+            if (scores.Single() is SoloScore single)
+            {
+                Debug.Assert(single.beatmap_id == candidate.beatmap_id);
+                preservedAlternatives = new HashSet<SoloScore> { single };
+                return true;
+            }
+
+            preservedAlternatives = new HashSet<SoloScore>(4);
 
             // TODO: this can likely be optimised (to not recalculate every score, in the case there's many candidates per beatmap).
             if (scores.MaxBy(s => s.pp) is SoloScore maxPPScore)