Steps to Reproduce:

1. Create a page
2. Make an edit to the page
3. Use an account with rollback permissions to view the diff between the creation edit and the later edit

Actual Results:
The rollback link is visible. However, attempting the rollback will fail since "last contributor is only author of this page."

Expected Results:
The rollback link should not be shown. Hiding the link would be consistent with the history page.