MAGETWO-62168: Improve field data converter logging and error reporting

Author: slopukhov

lib/internal/Magento/Framework/DB/DataConverter/SerializedToJson.php

@@ -65,6 +65,8 @@ protected function isValidJsonValue($value)
         ) {
             return true;
         }
+        //JSON last error reset
+        json_encode([]);
         return false;
     }