(ITS#3552) ldap_cancel_s or ldap_extended_operation_s is broken

[hyc@OpenLDAP.org]

Full_Name: Howard Chu
Version: 2.2,2.3,HEAD
OS: Linux
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (24.126.120.178)
Submitted by: hyc


In libraries/libldap/cancel.c ldap_cancel_s calls ldap_extended_operation_s()
with NULL for the last two arguments. But ldap_extended_operation_s() has an
assert() that requires at lease one of these two arguments to be non-NULL.
Judging from the remainder of the code, I think the assert() should be removed,
but not totally sure.