mod_ldap: Fix PR 36563. Keep track of the number of attributes retrieved from...

mod_ldap: Fix PR 36563. Keep track of the number of attributes retrieved from LDAP so that all of the values can be properly cached even if the value is NULL.

Reviewed by: bnicholes, minfrin, jim

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@291123 13f79535-47bb-0310-9956-ffa450edef68