If ldap sync is run while ldap is misconfigured, it can end up causing
troublesome deactivations due to not finding users in ldap -
deactivating all users, or deactivating all administrators of a realm,
which then will require manual intervention to reactivate at least one
admin in django shell.
This change prevents such potential troublesome situations which are
overwhelmingly likely to be unintentional. If intentional, --force
option can be used to remove the protection.