Plugin uninstall has fatal error

[jom]

It looks like this might be caused, possibly, by accessing terms through trash -> lesson order -> course structure after the taxonomy has been removed.

Steps to Reproduce

1. Create a course with a module and lessons.
2. Enable option to delete data on uninstall.
3. Deactivate and uninstall the plugin.

What I Expected

The plugin to be uninstalled

What Happened Instead

Fatal error.

PHP / WordPress / Sensei LMS version

PHP 7.4 / WP 5.6 / Sensei LMS 3.8.1

Work around

Trash all courses and lessons before deleting Sensei

Example Debug Log

Notice: Trying to get property 'term_id' of non-object in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-modules.php on line 1489 
Notice: Trying to get property 'term_id' of non-object in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-modules.php on line 1489 
Notice: Undefined index: term_id in /srv/htdocs/__wp__/wp-includes/class-wp-list-util.php on line 161 
Notice: Undefined index: term_id in /srv/htdocs/__wp__/wp-includes/class-wp-list-util.php on line 161 
Notice: Trying to get property 'term_id' of non-object in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-modules.php on line 1489 
Notice: Trying to get property 'term_id' of non-object in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-modules.php on line 1489 

Fatal error: Uncaught TypeError: Argument 1 passed to Sensei_Course_Structure::prepare_module() must be an instance of WP_Term, array given, called in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-course-structure.php on line 84 and defined in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-course-structure.php:121 
Stack trace: 
#0 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-course-structure.php(84): Sensei_Course_Structure->prepare_module(Array, 'any') 
#1 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-admin.php(1581): Sensei_Course_Structure->get('edit') 
#2 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-admin.php(1536): Sensei_Admin->get_course_structure(46)
#3 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-lesson.php(462): Sensei_Admin->save_lesson_order('', 46) 
#4 /srv/htdocs/__wp__/wp-includes/class-wp-hook.php(289): Sensei_Lesson->add_lesson_to_course_order(47) 
#5 /srv/htdocs/__wp__/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(false, Array) 
#6 /srv/htdocs/__wp__/wp-includes/plugin.php(484): WP_Hook->do_action(Array) 
#7 /srv/htdocs/__wp__/wp-includes/post.php(4309): do_action('save_post', 47, Object(WP_Post), true) 
#8 /srv/htdocs/__wp__/wp-includes/post.php(4411): wp_insert_post(Array, false, true) 
#9 /srv/htdocs/__wp__/wp-includes/post.php(3222): wp_update_post(Array) 
#10 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-data-cleaner.php(284): wp_trash_post(47) 
#11 /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-data-cleaner.php(257): Sensei_Data_Cleaner::cleanup_custom_post_types() 
#12 /srv/htdocs/wp-content/plugins/sensei-lms/uninstall.php(43): Sensei_Data_Cleaner::cleanup_all() 
#13 /srv/htdocs/__wp__/wp-admin/includes/plugin.php(1261): include_once('/srv/htdocs/wp-...') 
#14 /srv/htdocs/__wp__/wp-admin/includes/plugin.php(967): uninstall_plugin('sensei-lms/sens...') 
#15 /srv/htdocs/__wp__/wp-admin/includes/ajax-actions.php(4573): delete_plugins(Array) 
#16 /srv/htdocs/__wp__/wp-includes/class-wp-hook.php(287): wp_ajax_delete_plugin('') 
#17 /srv/htdocs/__wp__/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters('', Array) 
#18 /srv/htdocs/__wp__/wp-includes/plugin.php(484): WP_Hook->do_action(Array) 
#19 /srv/htdocs/__wp__/wp-admin/admin-ajax.php(184): do_action('wp_ajax_delete-...')
#20 {main} thrown in /srv/htdocs/wp-content/plugins/sensei-lms/includes/class-sensei-course-structure.php on line 121

[donnapep]

Fixed by #4128.