### 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.
}
				atidx = k;
				break;
			}
			if (atidx == -1) {
				
				for (WindowWrapper *wrapper : floating_docks) {
					if (wrapper->get_meta("dock_name") == name) {
						if (restore_window_on_load && floating_docks_dump.has(name)) {
							_restore_floating_dock(floating_docks_dump[name], wrapper, i);
							return;
						} else {
							_dock_floating_close_request(wrapper);
							atidx = wrapper->get_meta("dock_index");
						}
					}
				}
				
				continue;
			}
			if (atidx == i) {
				dock_slot[i]->move_child(node, 0);
			} else if (atidx != -1) {
				dock_slot[atidx]->remove_child(node);
				if (dock_slot[atidx]->get_tab_count() == 0) {
					dock_slot[atidx]->hide();
				}
				dock_slot[i]->add_child(node);
				dock_slot[i]->move_child(node, 0);
				dock_slot[i]->set_tab_title(0, TTRGET(node->get_name()));