### 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.
if (waiting_for_first_scan) {
		waiting_for_first_scan = false;
		OS::get_singleton()->benchmark_end_measure("editor_scan_and_import");
		
		
		RenderingServer::get_singleton()->global_shader_parameters_load_settings(true);
		
		if (!singleton->cmdline_export_mode) {
			EditorResourcePreview::get_singleton()->start();
		}
		_load_editor_layout();
		if (!defer_load_scene.is_empty()) {
			OS::get_singleton()->benchmark_begin_measure("editor_load_scene");
			load_scene(defer_load_scene);
			defer_load_scene = "";
			OS::get_singleton()->benchmark_end_measure("editor_load_scene");
			OS::get_singleton()->benchmark_dump();
		}
	}
}
void EditorNode::_scan_external_changes() {