escape image URL

git-svn-id: https://plugins.svn.wordpress.org/xml-sitemap-feed/trunk@973899 b8457f37-d9ea-0310-8a92-e5e31aec5664
escape image URL

git-svn-id: https://plugins.svn.wordpress.org/xml-sitemap-feed/trunk@973902 b8457f37-d9ea-0310-8a92-e5e31aec5664