metadata_exists() returns incorrect value when "get_{$meta_type}_metadata" filter returns false.

[jsmoriss]

metadata_exists() applies the "get_{$meta_type}_metadata" filter. If the $single metadata value is false, 0, an empty string, or an empty array (see ​https://www.php.net/manual/en/language.types.boolean.php), then metadata_exists() will return false instead of true (ie. the metadata exists).

function metadata_exists( $meta_type, $object_id, $meta_key ) {
.
.
.
        $check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, true, $meta_type );
        if ( null !== $check ) {
                return (bool) $check;
        }

If any value is returned, then the metadata exists, so the code should be:

function metadata_exists( $meta_type, $object_id, $meta_key ) {
.
.
.
        $check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, true, $meta_type );
        if ( null !== $check ) {
                return true;
        }

js.