Do not attempt to match score by equality of hash if it's empty

Closes ppy#28216.

The affected user's database contained six sentakki scores with an empty
hash. When an online score is being imported, an online model (which
does not have a hash) will be transmogrified into a `ScoreInfo` with
an empty hash, which would end up accidentally matching those scores
and basically breaking everything at that point.

To fix, avoid attempting to match anything on empty hash. This does not
break online score matching because for those cases the actual online ID
of the score will be used.

osu.Game/Scoring/ScoreManager.cs

@@ -88,7 +88,7 @@ public ScoreManager(RulesetStore rulesets, Func<BeatmapManager> beatmaps, Storag
         {
             ScoreInfo? databasedScoreInfo = null;
 
-            if (originalScoreInfo is ScoreInfo scoreInfo)
+            if (originalScoreInfo is ScoreInfo scoreInfo && !string.IsNullOrEmpty(scoreInfo.Hash))
                 databasedScoreInfo = Query(s => s.Hash == scoreInfo.Hash);
 
             if (originalScoreInfo.OnlineID > 0)