### 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.
List<String> scenes;
	int current_tab = scene_tabs->get_current_tab();
	for (int i = 0; i < p_resources.size(); i++) {
		String file_type = ResourceLoader::get_resource_type(p_resources[i]);
		if (file_type == "PackedScene") {
			scenes.push_back(p_resources[i]);
			
			continue;
		}
		if (!ResourceCache::has(p_resources[i])) {
			
			continue;
		}
		
		Ref<Resource> resource = ResourceCache::get_ref(p_resources[i]);
		if (resource.is_valid()) {
			resource->reload_from_file();
		}
	}
	for (const String &E : scenes) {
		reload_scene(E);
		reload_instances_with_path_in_edited_scenes(E);
	}
	scene_tabs->set_current_tab(current_tab);
}
void EditorNode::_sources_changed(bool p_exist) {