baseldap: Properly handle the case of renaming object to the same name
When renaming a object to the same name, errors.EmptyModList is raised.
This is not properly handled, and can cause other modifications in the
LDAPUpdate command to be ignored.
https://fedorahosted.org/freeipa/ticket/4548
Reviewed-By: Jan Cholasta <jcholast@redhat.com>