MDL-75218 introduced the Favicon (core_admin | favicon) setting. But if you upload a file in .ico format, for example favicon.ico, then no favicon is displayed for the page.

Steps to reproduce issue

1. Download a working .ico file (for example: wget https://sandbox.moodledemo.net/theme/image.php/boost/theme/-1/favicon).
2. Log into Moodle as a site admin and go to Site administration > Appearance > Logos.
3. Upload a file for the Favicon setting selecting the icon downloaded in step 1.
4. Click Save changes.

Expected results

The favicon is now displayed in the browser for this site.

Actual results

A favicon is no longer displayed in the browser for this site.