mod_ldap: Make LDAPSharedCacheSize 0 create a non-shared-memory cache per

process as opposed to disabling caching completely. This allows to use
the non-shared-memory cache as a workaround for the shared memory cache
not being available during graceful restarts

PR: 48958


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1096577 13f79535-47bb-0310-9956-ffa450edef68