Sticking a post makes other sticky posts unsticked

[takayukister]

• is_admin() returns false when used in a REST API flow, even when the API request is made on an admin page.
• In stick_post(), get_option( 'sticky_posts' ) is called. This then calls bogo_option_sticky_posts() which reduces $stickies posts. This is the direct cause of this issue.
• The intention Bogo adds a filter for the sticky posts option is to show only sticky posts in the current locale.
• In wp-includes/class-wp-query.php, WordPress puts sticky posts at the top of the posts array. WP does it only when is_home is true.
• So, is_home() check can be used as a better alternative than is_admin().