division-by-zero bug removed

git-svn-id: https://plugins.svn.wordpress.org/wp-einsatz/trunk@820476 b8457f37-d9ea-0310-8a92-e5e31aec5664
version 3.8 tested

git-svn-id: https://plugins.svn.wordpress.org/wp-einsatz/trunk@820477 b8457f37-d9ea-0310-8a92-e5e31aec5664