### 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)

color = get_theme_color(is_read_only() ? SNAME("readonly_warning_color") : SNAME("warning_color"));
			} else {
				color = get_theme_color(is_read_only() ? SNAME("readonly_color") : SNAME("property_color"));
			}
			if (label.contains(".")) {
				
				
				color.a = 0.5;
			}
			int ofs = get_theme_constant(SNAME("font_offset"));
			int text_limit = text_size - ofs;
			if (checkable) {
				Ref<Texture2D> checkbox;
				if (checked) {
					checkbox = get_theme_icon(SNAME("GuiChecked"), SNAME("EditorIcons"));
				} else {
					checkbox = get_theme_icon(SNAME("GuiUnchecked"), SNAME("EditorIcons"));
				}
				Color color2(1, 1, 1);
				if (check_hover) {
					color2.r *= 1.2;
					color2.g *= 1.2;
					color2.b *= 1.2;
				}
				check_rect = Rect2(ofs, ((size.height - checkbox->get_height()) / 2), checkbox->get_width(), checkbox->get_height());
				if (rtl) {
					draw_texture(checkbox, Vector2(size.width - check_rect.position.x - checkbox->get_width(), check_rect.position.y), color2);
				} else {
					draw_texture(checkbox, check_rect.position, color2);
				}