ensure api response is valid otherwise ignore response without crashing

git-svn-id: https://plugins.svn.wordpress.org/call-tracking-metrics/trunk@902182 b8457f37-d9ea-0310-8a92-e5e31aec5664
ready for release

git-svn-id: https://plugins.svn.wordpress.org/call-tracking-metrics/trunk@902185 b8457f37-d9ea-0310-8a92-e5e31aec5664