Font Library: fix PHPnotice "Undefined index: paged"

[matiasbenedetto]

A notice is being thrown related to the REST API anytime the Font Library UI is loaded:

PHP Notice:  Undefined index: paged in /site/path/wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php on line 394
PHP Stack trace:
...
PHP  13. WP_REST_Font_Families_Controller->get_items() /site/path/wp-includes/rest-api/class-wp-rest-server.php

It probably started when we updated the REST Controller to extend the Posts Controller.

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Issue originally reported by @jffng in #57569 (review)

[matiasbenedetto]

Closing this as outdated; this was already fixed.