3D FlipBook - Prevent direct calls of PHP files

I see the following Warning and Errors in the Logs:

PHP Warning: Attempt to read property "prefix" on null in /wp-content/plugins/interactive-3d-flipbook-powered-physics-engine/index.php on line 50 PHP Fatal error: Uncaught Error: Call to undefined function iberezansky\fb3d\plugin_dir_path() in /wp-content/plugins/interactive-3d-flipbook-powered-physics-engine/index.php:91

These are caused by direct calls from hackers and crawlers. For security reasons please prevent direct calls of all of your plugin's files by simply adding this oneliner at the beginning of your files.

defined( 'ABSPATH' ) || die();