Handle error response with empty body

[gapple]

The current code:

  if (is_array($content)) {
    $error = $content[0];
    if (400 == $response->getStatusCode()) {

doesn't handle if the response is an empty array, and ends up causing an "Undefined offset: 0" exception that masks the error from the API. I encountered this in a couple circumstances, typically with a 500 error that wasn't handled meaningfully either.

This probably needs some improvement, but it at least allowed me to handle errors a little better in my application.