Move difficulty copy to `BeatmapModelManager.Save`

osu.Game/Beatmaps/BeatmapModelManager.cs

@@ -192,6 +192,8 @@ public virtual void Save(BeatmapInfo beatmapInfo, IBeatmap beatmapContent, ISkin
         {
             var setInfo = beatmapInfo.BeatmapSet;
 
+            beatmapInfo.BaseDifficulty.CopyFrom(beatmapContent.Difficulty);
+
             using (var stream = new MemoryStream())
             {
                 using (var sw = new StreamWriter(stream, Encoding.UTF8, 1024, true))

osu.Game/Screens/Edit/Editor.cs

@@ -332,8 +332,6 @@ protected void Save()
             // no longer new after first user-triggered save.
             isNewBeatmap = false;
 
-            playableBeatmap.BeatmapInfo.BaseDifficulty.CopyFrom(playableBeatmap.Difficulty);
-
             // apply any set-level metadata changes.
             beatmapManager.Update(playableBeatmap.BeatmapInfo.BeatmapSet);