File module's FilemimeFormatter icon display renders empty image

For anyone applying this as a patch in the meantime: Note that this creates new files and because of this (https://github.com/cweagans/composer-patches/issues/514), setting a fixed patch level is mandatory, like so:

"extra": {
    "composer-patches": {
        "package-depths": {
            "drupal/core": 2
        },
        "comment": "The above is already in preparation for composer-patches v2"
    },
    "patchLevel": {
        "drupal/core": "-p2",
        "comment": "Or else we get files created everywhere, see https://github.com/cweagans/composer-patches/issues/514"
    },