Account for a WP_Error result from Google Suggest request

If a request fails and the result is a WP_Error object, a fatal
error is thrown when attempting to access the result as an array.

This wraps the processing of the response in a check for the error
and results in an empty return array if one is found.

It may be beneficial to provide some sort of error message on the
front end.
Merge pull request #1039 from jeremyfelt/error/ajax

Account for a WP_Error result from Google Suggest request