Start with a fresh beatmap when entering editor from main menu

osu.Game/Beatmaps/BeatmapManager_WorkingBeatmap.cs

@@ -33,6 +33,9 @@ namespace osu.Game.Beatmaps
 
             protected override IBeatmap GetBeatmap()
             {
+                if (BeatmapInfo.Path == null)
+                    return BeatmapInfo.Ruleset.CreateInstance().CreateBeatmapConverter(new Beatmap()).Beatmap;
+
                 try
                 {
                     using (var stream = new LineBufferedReader(store.GetStream(getPathForFile(BeatmapInfo.Path))))