fix a problem in memory handling in myldap_get_values_len() if malloc() would fail (r1909 from 0.9)

git-svn-id: http://arthurdejong.org/svn/nss-pam-ldapd/nss-pam-ldapd-0.8@1932 ef36b2f9-881f-0410-afb5-c4e39611909c