Only show header if there are related posts (content filter)

git-svn-id: https://plugins.svn.wordpress.org/related/trunk@962250 b8457f37-d9ea-0310-8a92-e5e31aec5664
Really Tag 1.5.2

git-svn-id: https://plugins.svn.wordpress.org/related/trunk@962253 b8457f37-d9ea-0310-8a92-e5e31aec5664