CRED form shortcode causes Post Snippets fatal error

Adding function_exists to get_current_screen() works so I submitted https://github.com/artstorm/post-snippets/pull/52

I believe the issue is due to CRED form displaying TinyMCE editor in its own custom way.

Additional note from https://codex.ww.wp.xz.cn/Function_Reference/get_current_screen#Usage_Restrictions

Usage Restrictions
This function is defined on most admin pages, but not all. Thus there are cases where is_admin() will return true, but attempting to call get_current_screen() will result in a fatal error because it is not defined. One known example is wp-admin/customize.php.

🙂