Changing visibility resets unsaved URL changes

[mootari]

Describe the bug

On a notebook that is unlisted and has an automatic URL:

1. Open publish settings
2. Change option "Notebook URL" to "Custom"
3. Enter a slug
4. Change option "Visibility" to "Public"

Expected behavior

Notebook URL retains changes. Instead it gets reset to "Automatic", and the edit is lost.