ldap: test for empty attributes list

ldap: test for empty attributes list

Test for LDAP request with an empty attribute list.  LDB responds with
no attributes, but LDAP responds with all attributes.  Fix is attached
to the bug below but we can't push it upstream until we've found all
instances of incorrect empty attribute list usage in Samba.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13852

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>