Manual grading page is broken when Question per page is set incorrectly.
- Create a course.
- Create a quiz activity.
- Add an "Essay" question.
- Login as a student, and submit the quiz.
- Login as teacher, go to Manual grading screen.
- Press "grade" link to make a grade.
- Set 0 in "Questions per page" in "Options", and press "Change options".
- The error "Coding error detected, it must be fixed by a programmer: moodle_database::get_in_or_equal() does not accept empty arrays" is shown, and the user cannot manual grade any more.