Ticket 571 - server does not accept 0 length LDAP Control sequence
Bug Description: If we receive an incorrect control, with non NULL bv_val but
bv_len=0, it can trigger a crash. This bug occurs because
of a call of openldap ber_init with such incorrect control.
Fix Description: Before calling ber_init, check that the control length is not 0.
https://fedorahosted.org/389/ticket/571
Reviewed by richm(Thanks!)