fix crash when retrieving large networks entries (8532f40 from 0.9, thanks Lukas Slebodnik)

git-svn-id: http://arthurdejong.org/svn/nss-pam-ldapd/nss-pam-ldapd-0.8@2067 ef36b2f9-881f-0410-afb5-c4e39611909c