mod_ldap: Fix the search limit parameter to ldap_search_ext_s()

for SDKs that define LDAP_NO_LIMIT to something other than -1.

Submitted by: David Jones <oscaremma gmail.com>
Reviewed by:  trawick



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@509237 13f79535-47bb-0310-9956-ffa450edef68