Users: Disallow bulk editing a single user with no roles.

This changeset prevents users from removing their own role when bulk editing user roles.

Props jomonthomaslobo1, johnbillion, hugod, audrasjb, shailu25, rishavdutta, rollybueno.
Fixes #63068.



git-svn-id: https://develop.svn.wordpress.org/trunk@62026 602fd350-edb4-49c9-b593-d223f7449a82