Improve error handing if using CKAN API client for a Socrata data catalog

Socrata returns JSON where the "error" key is a boolean. The CKAN API client expects the "error" key to be a dictionary. If "error" is not a dictionary, this PR makes it an empty dictionary.

Without this PR, you get `AttributeError: 'bool' object has no attribute 'get'`, which is totally opaque.