paging_bar previous/next buttons have wrong page numbers

Requirements

1. A course with at least 100 enrolments. Can use:

   php admin/tool/generator/cli/maketestcourse.php --shortname=MDL-68427 --size=S

Testing

1. Apply the attached patch (0001-DO-NOT-COMMIT.patch):

   git am /path/to/0001-DO-NO-COMMIT.patch

2. View the course page
3. Choose "Participants" from the drawer on the left
4. Edit the URL by changing the perpage=20 to perpage=5 or add &perpage=5 if the parameter is missing and ensure you press enter to load the page
   1. Confirm that the pagination links show the current page as page 1
   2. *Confirm that there is no "Previous page" button (with a label like <<)
   3. Confirm that the "Next page" button is labelled ">> (2)"
   4. Confirm that there is a "Last page" which just as the final page number after a ...
5. Click on the Next page button
   1. Confirm that the pagination links show the current page as page 2
   2. Confirm that the "Previous page" button is labelled "<< (1)"
   3. Confirm that the "Next page" button is labelled ">> (3)"
   4. Confirm that there is a "Last page" which just as the final page number after a ...
6. Click on the "Last page" button
   1. Confirm that the pagination links show the current page as the number that you clicked
   2. Confirm that the "Previous page" button is labelled "<< ([previous page number])"
   3. Confirm that there is no "Next page" button
   4. Confirm that there is a "First page" which just as "1" and that there is a ... marked before another page number