Fix bug with exclusive facets when there is only one

git-svn-id: https://plugins.svn.wordpress.org/opensearchserver-search/trunk@1021525 b8457f37-d9ea-0310-8a92-e5e31aec5664
Version 1.4.1

git-svn-id: https://plugins.svn.wordpress.org/opensearchserver-search/trunk@1021526 b8457f37-d9ea-0310-8a92-e5e31aec5664