### 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 (_initializing_plugins) {
		return;
	}
	Vector<String> enabled_addons;
	for (const KeyValue<String, EditorPlugin *> &E : addon_name_to_plugin) {
		enabled_addons.push_back(E.key);
	}
	if (enabled_addons.size() == 0) {
		ProjectSettings::get_singleton()->set("editor_plugins/enabled", Variant());
	} else {
		enabled_addons.sort();
		ProjectSettings::get_singleton()->set("editor_plugins/enabled", enabled_addons);
	}
	project_settings_editor->queue_save();
}
void EditorNode::set_addon_plugin_enabled(const String &p_addon, bool p_enabled, bool p_config_changed) {
	String addon_path = p_addon;
	if (!addon_path.begins_with("res:")) {
		addon_path = "res:addons/" + addon_path + "/plugin.cfg";
	}
	ERR_FAIL_COND(p_enabled && addon_name_to_plugin.has(addon_path));
	ERR_FAIL_COND(!p_enabled && !addon_name_to_plugin.has(addon_path));
	if (!p_enabled) {
		EditorPlugin *addon = addon_name_to_plugin[addon_path];
		remove_editor_plugin(addon, p_config_changed);
		memdelete(addon);
		addon_name_to_plugin.erase(addon_path);
		_update_addon_config();
		return;
	}