Fix notices seen with WP_DEBUG enabled

git-svn-id: https://plugins.svn.wordpress.org/featured-image-zoom/trunk@838999 b8457f37-d9ea-0310-8a92-e5e31aec5664
Stable tag: 1.0.1

git-svn-id: https://plugins.svn.wordpress.org/featured-image-zoom/trunk@839001 b8457f37-d9ea-0310-8a92-e5e31aec5664