Fix scene deletion code to match master's behavior.

Previous code, while more correct than old master one, could still lead
to invalid state in some corner cases (like linked scenes...).

source/blender/editors/scene/scene_edit.c

@@ -104,7 +104,11 @@ bool ED_scene_delete(bContext *C, Main *bmain, wmWindow *win, Scene *scene)
 	WM_window_change_active_scene(bmain, C, win, scene_new);
 
 	BKE_libblock_remap(bmain, scene, scene_new, ID_REMAP_SKIP_INDIRECT_USAGE | ID_REMAP_SKIP_NEVER_NULL_USAGE);
-	BKE_libblock_free(bmain, scene);
+
+	id_us_clear_real(&scene->id);
+	if (scene->id.us == 0) {
+		BKE_libblock_free(bmain, scene);
+	}
 
 	return true;
 }