issuing an invite as a non-admin user gives an 'access denied'

As a user with none of the Invite module's permissions, I can still see the invite block (that's perhaps another bug too... but for another issue).

When I submit the form, I get a confirmation message, but I am taken to the Invite entity page which shows an access denied message.

The form redirection should check whether the user has access or not, and if not, keep them on the same page they started on.