Deleting a course that's been starred causes ' invalidrecord: Can't find data record in database table course.' error

Upgrade test.

1. Clone a fresh site, but do not install yet.
2. For each branch, we first need to set up a failure state, based on the latest weekly, so please run the following:
   For master:

   git checkout a672f021eaf0

   For 37:

   git checkout 6a30269d98d8

   For 36:

   git checkout 7de0c0f1ad6

3. Now, as admin, install the site
4. Make sure debugging is set to developer.
5. Create two courses (c1 and c2) and a user (s1)
6. Enrol a user (s1) into c1 and c2 as a student
7. Log out.
8. Log in as s1
9. view the dashboard
10. Add the 'Starred courses' block and the 'Course overview' block if they're not already present.
11. From the 'Course overview' block, using the ellipsis (...) menu next to the course c1, select 'Star this course'.
12. Do the same for c2.
13. Log out
14. Log in as an admin
15. From site admin -> course management, delete the course c1
16. Log out
17. Log in as the student s1
18. Go to the dashboard
19. Verify you see an error popup. This is the bug.
20. Log out
21. Now, checkout the relevant head to trigger the upgrade:
    For master:

    git checkout master

    For 37:

    git checkout MOODLE_37_STABLE

    For 36:

    git checkout MOODLE_36_STABLE

22. Log in as admin and run the upgrade.
23. Log out
24. Log in as the student s1.
25. Go to the dashboard
26. Verify you see no error popup
27. Verify you see c2 listed in the 'Starred courses' block.

Course deletion hook test

1. Log in as admin
2. Create a new course c3 and enrol s1 into it as a student
3. Log out
4. Log in as the student s1
5. Go to the dashboard
6. From the 'Course overview' block, using the ellipsis (...) menu next to the course c3, select 'Star this course'.
7. Log out
8. Log in as admin
9. From site admin -> course management, delete the course c3
10. Log out
11. Log in as the student s1
12. Go to the dashboard
13. Verify you see no error popup
14. Verify you don't see the course c3 listed in the 'Starred courses' block.
15. Verify you see c2 listed in the 'Starred courses' block.