### Godot version

4.1 beta2

### System information

Windows 10 Home

### Issue description

I had a control with a custom theme which i removed. When loading the project again the Theme Editor is opened and some actions, like Show Default or Override All, cause the editor to crash.

### Steps to reproduce

1. create a scene with a Control node
2. add a custom theme to it
3. click the theme so the Theme Editor opens
4. remove the theme
5. save the scene
6. close the project and open it again (Theme Editor needs to be opened when closing the project)
7. click Show Default or Override All

### Minimal reproduction project

[Godot41_themeEditorCrash.zip](https://github.com/godotengine/godot/files/11760454/Godot41_themeEditorCrash.zip)

void _update_addon_config();
	void _toggle_distraction_free_mode();
	void _inherit_imported(const String &p_action);
	void _open_imported();
	void _update_update_spinner();
	void _resources_changed(const Vector<String> &p_resources);
	void _scan_external_changes();
	void _reload_modified_scenes();
	void _reload_project_settings();
	void _resave_scenes(String p_str);
	void _feature_profile_changed();
	bool _is_class_editor_disabled_by_feature_profile(const StringName &p_class);
	Ref<Texture2D> _get_class_or_script_icon(const String &p_class, const Ref<Script> &p_script, const String &p_fallback = "Object");
	void _pick_main_scene_custom_action(const String &p_custom_action_name);
	void _immediate_dialog_confirmed();
	void _select_default_main_screen_plugin();
	void _bottom_panel_switch(bool p_enable, int p_idx);
	void _bottom_panel_raise_toggled(bool);
	void _begin_first_scan();
protected:
	friend class FileSystemDock;
	static void _bind_methods();
	void _notification(int p_what);
	int get_current_tab();
	void set_current_tab(int p_tab);
public:
	
	void _on_plugin_ready(Object *p_script, const String &p_activate_name);
	void editor_select(int p_which);
	void set_visible_editor(EditorTable p_table) { editor_select(p_table); }