mod_ldap: Fix regression in handling "server unavailable" errors on

Windows. Followup to r1375696.

PR 54140.

Backport of r1408402 from trunk resp. r1409773 from 2.4.x.

Submitted by: covener
Reviewed by: wrowe, rjung
Backported by: covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@1445119 13f79535-47bb-0310-9956-ffa450edef68