### 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)

Ref<Texture2D> arrow;
	if (foldable) {
		if (object->editor_is_section_unfolded(section)) {
			arrow = get_theme_icon(SNAME("arrow"), SNAME("Tree"));
		} else {
			if (is_layout_rtl()) {
				arrow = get_theme_icon(SNAME("arrow_collapsed_mirrored"), SNAME("Tree"));
			} else {
				arrow = get_theme_icon(SNAME("arrow_collapsed"), SNAME("Tree"));
			}
		}
	}
	return arrow;
}
int EditorInspectorSection::_get_header_height() {
	Ref<Font> font = get_theme_font(SNAME("bold"), SNAME("EditorFonts"));
	int font_size = get_theme_font_size(SNAME("bold_size"), SNAME("EditorFonts"));
	int header_height = font->get_height(font_size);
	Ref<Texture2D> arrow = _get_arrow();
	if (arrow.is_valid()) {
		header_height = MAX(header_height, arrow->get_height());
	}
	header_height += get_theme_constant(SNAME("v_separation"), SNAME("Tree"));
	return header_height;
}
void EditorInspectorSection::_notification(int p_what) {