Check if file is readable before include

git-svn-id: https://plugins.svn.wordpress.org/twig/trunk@963863 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed file path

git-svn-id: https://plugins.svn.wordpress.org/twig/trunk@963872 b8457f37-d9ea-0310-8a92-e5e31aec5664