Preload Fonts: installation subfolder name is stripped from URLs

[girlie]

When saving URLs to Preload Fonts, the domain name is stripped automatically -- but in the case of a subdirectory installation, the subfolder name is also being removed, which results in an invalid URL being preloaded on the front end.

1. Must have WordPress Site URL located in a subfolder, e.g., https://example.com/sub/
2. Need at least one font URL to test, e.g., https://example.com/sub/wp-content/themes/twentytwenty/assets/fonts/inter/Inter-upright-var.woff2
3. Add the URL to the Preload Fonts field, then save the change.
4. See that the subfolder has also been removed from the URL:

5. On the front end, the domain will be added back, but not the subfolder:

<link rel="preload" as="font" href="https://example.com/wp-content/themes/twentytwenty/assets/fonts/inter/Inter-upright-var.woff2" crossorigin>

6. Thus, the font's URL is invalid and it cannot actually be preloaded.

Related: https://secure.helpscout.net/conversation/2438758491/461019/