### Godot version

4.1.beta (7b1387ff2)

### System information

Mageia 9, Linux

### Issue description

When opening an empty project in latest `master`, I get these errors:
```
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: get_scene_path (editor/scu/../editor_data.cpp:880)
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: check_and_update_scene (editor/scu/../editor_data.cpp:683)
ERROR: Index p_idx = -1 is out of bounds (edited_scene.size() = 1).
   at: set_edited_scene (editor/scu/../editor_data.cpp:745)
```

Possibly related to recent changes to restore past sessions, but there's nothing to restore in this case?

### Steps to reproduce

- Create a new project, edit it
- Quit to project manager
- Re-open the newly created project -> errors

### Minimal reproduction project

Empty project.
bool all_saved = true;
	for (int i = 0; i < editor_data.get_edited_scene_count(); i++) {
		Node *scene = editor_data.get_edited_scene_root(i);
		if (scene) {
			if (!scene->get_scene_file_path().is_empty() && DirAccess::exists(scene->get_scene_file_path().get_base_dir())) {
				if (i != editor_data.get_edited_scene()) {
					_save_scene(scene->get_scene_file_path(), i);
				} else {
					_save_scene_with_preview(scene->get_scene_file_path());
				}
			} else if (!scene->get_scene_file_path().is_empty()) {
				all_saved = false;
			}
		}
	}
	if (!all_saved) {
		show_warning(TTR("Could not save one or more scenes!"), TTR("Save All Scenes"));
	}
	save_default_environment();
}
void EditorNode::_mark_unsaved_scenes() {