Fix a potential segfault if the bind password in the LDAP cache

is NULL.
PR:	26686
Obtained from:
Submitted by:	Jari Ahonen <jah@progress.com>
Reviewed by:	jim, trawick, bnicholes, minfrin


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/APACHE_2_0_BRANCH@103732 13f79535-47bb-0310-9956-ffa450edef68