test $post to see if it's an object before using it

git-svn-id: https://plugins.svn.wordpress.org/jm-dashicons-shortcode/trunk@872392 b8457f37-d9ea-0310-8a92-e5e31aec5664
edit changelog

git-svn-id: https://plugins.svn.wordpress.org/jm-dashicons-shortcode/trunk@872394 b8457f37-d9ea-0310-8a92-e5e31aec5664