Add some sanity checking

We're checking if $graphdata was a valid JSON string ($response will be false if it wasn't), we check if $response is an array and if the "likes" key is actually set.

fblikes.snippet.php

@@ -43,6 +43,9 @@
 	$graphdata = file_get_contents("http://graph.facebook.com/".$pageid);
 	// decode json response
 	$response = $modx->fromJSON($graphdata);
+	if (!$response || !is_array($response) || !isset($response['likes'])) {
+		return 'Data currently not available.';
+	}
 	// get like number
 	$data = $response['likes'];