When students click on the 'View grades' button, they cannot see the marking guide descriptions for a Forum using Whole Forum Grading, even though 'show guide definition to students'  is enabled in the marking guide setup.

Staff can view the description by clicking on the small 'i' icon, but this icon is greyed out for students.

Step to reproduce the issue:

1. Create a course.
2. Create a forum activity.
3. In "Whole forum grading" setting in the forum activity, Set
   Grade Type: Point
   Maximum grade: 100
   Grading method: Marking guide
4. Go to "Advanced grading" page, from cog icon in forum page.
5. Click "Define new grading form from scratch" and create grading form with some texts in "Description for students" and "Show guide definition to students" on.
6. Login as student, make a forum post.
7. Login as teacher, click "Grade users" to make grading points. (Teacher can see the marking guide description by clicking "i" icon)
8. Login as student, click "View grades" to see the result. The student can see the grade score and comments, but cannot see the Marking Guide Description for students. The the small 'i' icon is greyed out.