### 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)

if (p_index >= begin_array_index && p_index < end_array_index) {
		return array_elements[p_index - begin_array_index].vbox;
	} else if (p_index < 0) {
		return vbox;
	} else {
		return nullptr;
	}
}
EditorInspectorArray::EditorInspectorArray(bool p_read_only) {
	read_only = p_read_only;
	set_mouse_filter(Control::MOUSE_FILTER_STOP);
	odd_style.instantiate();
	even_style.instantiate();
	rmb_popup = memnew(PopupMenu);
	rmb_popup->add_item(TTR("Move Up"), OPTION_MOVE_UP);
	rmb_popup->add_item(TTR("Move Down"), OPTION_MOVE_DOWN);
	rmb_popup->add_separator();
	rmb_popup->add_item(TTR("Insert New Before"), OPTION_NEW_BEFORE);
	rmb_popup->add_item(TTR("Insert New After"), OPTION_NEW_AFTER);
	rmb_popup->add_separator();
	rmb_popup->add_item(TTR("Remove"), OPTION_REMOVE);
	rmb_popup->add_separator();
	rmb_popup->add_item(TTR("Clear Array"), OPTION_CLEAR_ARRAY);