### 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)

ERR_FAIL_COND(p_event.is_null());
	if (!foldable) {
		return;
	}
	Ref<InputEventMouseButton> mb = p_event;
	if (mb.is_valid() && mb->is_pressed() && mb->get_button_index() == MouseButton::LEFT) {
		if (object->editor_is_section_unfolded(section)) {
			int header_height = _get_header_height();
			if (mb->get_position().y >= header_height) {
				return;
			}
		}
		accept_event();
		bool should_unfold = !object->editor_is_section_unfolded(section);
		if (should_unfold) {
			unfold();
		} else {
			fold();
		}
	} else if (mb.is_valid() && !mb->is_pressed()) {
		queue_redraw();
	}
}
VBoxContainer *EditorInspectorSection::get_vbox() {