When binding anonymously, credentials are still needed.

(closes issue #12601)
 Reported by: suretec
 Patches: 
       res_config_ldap.c.patch uploaded by suretec (license 70)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@118302 65c4cc65-6c06-0410-ace0-fbb531ad65f3