Queries the database for any published post and saves
a flag whether any published post exists or not.

function block_core_calendar_update_has_published_posts() {
	global $wpdb;
	$has_published_posts = (bool) $wpdb->get_var( "SELECT 1 as test FROM {$wpdb->posts} WHERE post_type = 'post' AND post_status = 'publish' LIMIT 1" );
	update_option( 'wp_calendar_block_has_published_posts', $has_published_posts );
	return $has_published_posts;
}