Commit 35c0754f failed to handle space-separated lists of alternative
hostnames in ldapserver, when building a URI for ldap_initialize()
(OpenLDAP).  Such lists need to be expanded to space-separated URIs.

Repair.  Back-patch to 11, to fix bug report #15495.

Author: Thomas Munro
Reported-by: Renaud Navarro
Discussion: https://postgr.es/m/15495-2c39fc196c95cd72%40postgresql.org