fix deletion of standalone shortcodes


git-svn-id: https://plugins.svn.wordpress.org/media-credit/trunk@1004753 b8457f37-d9ea-0310-8a92-e5e31aec5664
Release 2.3.1

git-svn-id: https://plugins.svn.wordpress.org/media-credit/trunk@1004756 b8457f37-d9ea-0310-8a92-e5e31aec5664