Comments of change request are not protected with comment right

It's currently not possible to prevent users to post comments on change requests, even guest users.
Reproduction step:

• on a fresh wiki, Guest user should not be allowed to post comment
• Go to an existing change request, try to post a comment

Expected result:

• the buttons are disabled and the backend does not allow to do it

Obtained result:

• the comment is immediately posted even if comment right is explicitely forbidden