### 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)

deselect_all_colors_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_colors_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_colors_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			select_constants_icon->set_texture(get_theme_icon(SNAME("MemberConstant"), SNAME("EditorIcons")));
			deselect_all_constants_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_constants_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_constants_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			select_fonts_icon->set_texture(get_theme_icon(SNAME("Font"), SNAME("EditorIcons")));
			deselect_all_fonts_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_fonts_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_fonts_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			select_font_sizes_icon->set_texture(get_theme_icon(SNAME("FontSize"), SNAME("EditorIcons")));
			deselect_all_font_sizes_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_font_sizes_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_font_sizes_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			select_icons_icon->set_texture(get_theme_icon(SNAME("ImageTexture"), SNAME("EditorIcons")));
			deselect_all_icons_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_icons_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_icons_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
			select_styleboxes_icon->set_texture(get_theme_icon(SNAME("StyleBoxFlat"), SNAME("EditorIcons")));
			deselect_all_styleboxes_button->set_icon(get_theme_icon(SNAME("ThemeDeselectAll"), SNAME("EditorIcons")));
			select_all_styleboxes_button->set_icon(get_theme_icon(SNAME("ThemeSelectAll"), SNAME("EditorIcons")));
			select_full_styleboxes_button->set_icon(get_theme_icon(SNAME("ThemeSelectFull"), SNAME("EditorIcons")));
		} break;
	}
}
void ThemeItemImportTree::_bind_methods() {
	ADD_SIGNAL(MethodInfo("items_imported"));
}
ThemeItemImportTree::ThemeItemImportTree() {