bug fix

git-svn-id: https://plugins.svn.wordpress.org/scroll-top-and-bottom/trunk@871759 b8457f37-d9ea-0310-8a92-e5e31aec5664
error fix

git-svn-id: https://plugins.svn.wordpress.org/scroll-top-and-bottom/trunk@871760 b8457f37-d9ea-0310-8a92-e5e31aec5664