Missing "next" on fourth page of users navigation in messages

Make a course and enrol some students (at least 4). Navigate to "Current course" > "Participants". Modify the URL by adding the param perpage=1 Verify it works as expected. Change perpage to some different values, verify it still works OK. Modify the file lib/outputcomponents.php - change paging_bar 's $maxdisplay propery to 4. Go back to the list and make sure that when you are on page 4 you still see the "Next" link. Try the same thing but with changing $maxdisplay to 3, 2 and 1. Verify page 3, 2 and 1 (respectively) display the "Next" link.