fix for warning

git-svn-id: https://plugins.svn.wordpress.org/facebook-shop-by-storeyacom/trunk@952129 b8457f37-d9ea-0310-8a92-e5e31aec5664
tagging 5.3

git-svn-id: https://plugins.svn.wordpress.org/facebook-shop-by-storeyacom/trunk@952130 b8457f37-d9ea-0310-8a92-e5e31aec5664