### Godot version

v4.0.beta17.mono.official [c40020513]

### System information

Window 11, Forward+, GTX 1060

### Issue description

Adding two theme variations in a row result to a  crash.

https://user-images.githubusercontent.com/93253123/217037249-1ce1d56d-beb6-4435-83ad-9f8a07fe0e96.mp4



### Steps to reproduce

1. Create a project.
2. Create a theme.
3. Double click to go in the theme editor.
4. Click on manage items buttons.
5. In the add type field type a name to add a type.
6. type another name to add a second type.
7. Crash.

### Minimal reproduction project

[ThemeVariationCrash.zip](https://github.com/godotengine/godot/files/10665863/ThemeVariationCrash.zip)

object = nullptr;
	main_vbox = memnew(VBoxContainer);
	main_vbox->set_h_size_flags(SIZE_EXPAND_FILL);
	main_vbox->add_theme_constant_override("separation", 0);
	add_child(main_vbox);
	set_horizontal_scroll_mode(SCROLL_MODE_DISABLED);
	changing = 0;
	search_box = nullptr;
	_prop_edited = "property_edited";
	set_process(false);
	property_focusable = -1;
	property_clipboard = Variant();
	get_v_scroll_bar()->connect("value_changed", callable_mp(this, &EditorInspector::_vscroll_changed));
	update_scroll_request = -1;
	if (EditorSettings::get_singleton()) {
		refresh_countdown = float(EDITOR_GET("docks/property_editor/auto_refresh_interval"));
	} else {
		
		refresh_countdown = 0.33;
	}
	ED_SHORTCUT("property_editor/copy_value", TTR("Copy Value"), KeyModifierMask::CMD_OR_CTRL | Key::C);
	ED_SHORTCUT("property_editor/paste_value", TTR("Paste Value"), KeyModifierMask::CMD_OR_CTRL | Key::V);
	ED_SHORTCUT("property_editor/copy_property_path", TTR("Copy Property Path"), KeyModifierMask::CMD_OR_CTRL | KeyModifierMask::SHIFT | Key::C);
}