Unable to re-add permissions if all permissions is removed and user is an administrator (not sysadmin)

Steps to reproduce

1. Log into Confluence with an administrator (not system administrator) account.
2. Remove all of the permissions from the Confluence Questions Permissions admin screen.

Once the admin user hits Save, they'll get a "You are not permitted to perform this operation" when the page reloads. From that point on it's impossible for a regular administrator to re-add the permissions, it has to be a system administrator. Given we don't grant customer accounts sysadmin privileges in OnDemand, this is problematic.