wldap32: Accept a NULL value in ldap_set_option.

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
http://testbot.winehq.org/JobDetails.pl?Key=10187

Your paranoid android.


=== WNT4WSSP6 (32 bit parse) ===
parse.c:120: Test failed: ldap_set_optionW failed 0x00000059

=== W2KPROSP4 (32 bit parse) ===
parse.c:120: Test failed: ldap_set_optionW failed 0x00000059