Fix for edit user as admin

* It fixes an issue where you where able to remove your own
  admin rights. This would result in a 404 error. fixes: #2283
* It fixes an issue where you would be able to block your own
  account on the edit page. This fix makes the behaviour the same
  as on the admin/users overview page
Merge pull request #6025 from jvanbaarsen/fix-for-admin-user-edit

Fix for edit user as admin