Fix php7.2 count() warning

E_WARNING: count(): Parameter must be an array or an object that implements Countable
in get_the_content called at /app/source/public/wp-includes/formatting.php (3688)
in wp_trim_excerpt called at /app/source/public/wp-includes/class-wp-hook.php (288)
in WP_Hook::apply_filters called at /app/source/public/wp-includes/plugin.php (208)
in apply_filters called at /app/source/public/wp-includes/post-template.php (412)
…ns/planet4-plugin-blocks/classes/controller/blocks/class-covers-controller.php (170)
 
Warning appears only on php7.2