REST API: Treat any falsy value as false in 'rest_allow_anonymous_comments'.

Extend the check in 'rest_allow_anonymous_comments' to accept any falsy value
(previously this was an explicit check for `false`).

One possible failure case is that a plugin developer forgets to include a
return value for some code path in their callback for this filter, leading to a
value of `null` which is currently treated like `true`.

Props joehoyle, jnylen0.

Fixes #39010.


git-svn-id: https://develop.svn.wordpress.org/trunk@39487 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/rest-api/endpoints/class-wp-rest-comments-controller.php

@@ -392,7 +392,7 @@ class WP_REST_Comments_Controller extends WP_REST_Controller {
 			 *                                 response.
 			 */
 			$allow_anonymous = apply_filters( 'rest_allow_anonymous_comments', false, $request );
-			if ( false === $allow_anonymous ) {
+			if ( ! $allow_anonymous ) {
 				return new WP_Error( 'rest_comment_login_required', __( 'Sorry, you must be logged in to comment.' ), array( 'status' => 401 ) );
 			}
 		}