"uslugify" breaks header anchors list

Description

Setting custom slugify function “uslugify” from pymodown breaks header anchors block at the right.

markdown_extensions:
    ...
    - toc:
          permalink: '#'
          slugify: !!python/name:pymdownx.slugs.uslugify
    ...

Expected behavior

When scrolling down headers are fading out. This gives a visual understanding of current position on the page.

Actual behavior

When scrolling, the browser console spams the following error:

Steps to reproduce the bug

1. In mkdocs.yml set a custom slugify function (“uslugify” in my case)
2. Add some cyrillic headers in index.md
3. Anchor links are not fading and the console spams the error when scrolling the page

[squidfunk]

Perfect! I will issue a release within the next few days. Until then, please use the current master.

[squidfunk]

Fix released as part of 3.3.0.