Response from CTP could be empty

### Description
In our projects, we sometimes receive the error because `payload.body.results` is null or undefined.
https://github.com/sphereio/sphere-node-sdk/blob/master/src/coffee/services/base.coffee#L409

We're not sure why does the response from platform is null. In order to investigate deeper, a check for this issue should be added to the code. It can be similar to this one: https://github.com/sphereio/sphere-product-import/pull/164/files#diff-d7b70bb31c9da8f845222653763558c7R722