User capabilities filter throws fatal error on comments

Fatal error: Uncaught Error: Call to undefined method LLMS_Achievement::get() in /path/to/wp/wp-content/plugins/lifterlms/includes/llms.functions.core.php:815
--
  | Stack trace:
  | #0 /path/to/wp/wp-content/plugins/lifterlms/includes/models/model.llms.instructor.php(226): llms_get_post_parent_course(Object(LLMS_Achievement))
  | #1 /path/to/wp/wp-content/plugins/lifterlms/includes/class.llms.user.permissions.php(110): LLMS_Instructor->is_instructor('4378')
  | #2 /path/to/wp/wp-content/plugins/lifterlms/includes/class.llms.user.permissions.php(78): LLMS_User_Permissions->edit_others_lms_content(Array, Array, Array)
  | #3 /path/to/wp/wp-includes/class-wp-hook.php(288): LLMS_User_Permissions->handle_caps(Array, Array, Array)
  | #4 /path/to/wp/wp-includes/plugin.php(208): WP_Hook->apply_filters(Array, Array)
  | #5 /path/to/wp/ in /path/to/wp/wp-content/plugins/lifterlms/includes/llms.functions.core.php on line 815


```
https://github.com/gocodebox/lifterlms/blob/cdbee2b4b3bfabf3339bd6870f3d3af8e9227da0/includes/class.llms.user.permissions.php#L19 filters `user_has_cap` which runs

https://github.com/gocodebox/lifterlms/blob/cdbee2b4b3bfabf3339bd6870f3d3af8e9227da0/includes/class.llms.user.permissions.php#L78 which calls `edit_others_lms_content` method

https://github.com/gocodebox/lifterlms/blob/cdbee2b4b3bfabf3339bd6870f3d3af8e9227da0/includes/class.llms.user.permissions.php#L110 which checks if the user is an instructor and passes the second argument (Object ID which ends up not being a post ID but a comment ID, see the markup above)

https://github.com/gocodebox/lifterlms/blob/41a238fd11b7c86e33bbbbc84f173ace92d26eed/includes/models/model.llms.instructor.php#L204 where we get the post type of the comment_ID which sometimes ends up being an Achievement (that's why this is so rare) and then

https://github.com/gocodebox/lifterlms/blob/41a238fd11b7c86e33bbbbc84f173ace92d26eed/includes/models/model.llms.instructor.php#L226 calls https://github.com/gocodebox/lifterlms/blob/5f48ab6d09863d8688d07dd24753c4bd8d830367/includes/llms.functions.core.php#L815 where the absence of the get method on LLMS_Achievements triggers a fatal error (https://github.com/gocodebox/lifterlms/blob/a1a6833c6e6bab57bf4356739463220e51f89408/includes/class.llms.achievement.php)

So, it seems unsafe to assume that the object ID (third parameter) will always be a post_ID and additional checks must be added to make sure that the filter isn't run on anything except posts. I'm not sure how to do that right now but logging this.