Make sure the map does not show if no event location is set

git-svn-id: https://plugins.svn.wordpress.org/combrite/trunk@897173 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update readme to reflect 3.9 compatibility

git-svn-id: https://plugins.svn.wordpress.org/combrite/trunk@897178 b8457f37-d9ea-0310-8a92-e5e31aec5664