Do not attempt to load gameplay scene if current beatmap is dummy

osu.Game.Tests/Visual/Navigation/TestSceneSkinEditorNavigation.cs

@@ -281,7 +281,6 @@ namespace osu.Game.Tests.Visual.Navigation
             AddStep("set dummy beatmap", () => Game.Beatmap.SetDefault());
 
             openSkinEditor();
-            switchToGameplayScene();
         }
 
         [Test]

osu.Game/Overlays/SkinEditor/SkinEditorOverlay.cs

@@ -140,6 +140,12 @@ namespace osu.Game.Overlays.SkinEditor
         {
             performer?.PerformFromScreen(screen =>
             {
+                if (beatmap.Value is DummyWorkingBeatmap)
+                {
+                    // presume we don't have anything good to play and just bail.
+                    return;
+                }
+
                 // If we're playing the intro, switch away to another beatmap.
                 if (beatmap.Value.BeatmapSetInfo.Protected)
                 {