Unhandled NotFound exception

[rossjones]

From demo.ckan.org, NotFound is raised by not handled which results in a crash.

The fix is probably to catch and handle it at https://github.com/ckan/ckanext-dcat/blob/master/ckanext/dcat/controllers.py#L58

 File "/usr/lib/ckan/demo/src/ckanext-dcat/ckanext/dcat/controllers.py", line 35, in read_dataset
    'format': _format})
  File "/usr/lib/ckan/demo/src/ckan/ckan/logic/__init__.py", line 429, in wrapped
   result = _action(context, data_dict, **kw)
 File "/usr/lib/ckan/demo/src/ckanext-dcat/ckanext/dcat/logic.py", line 24, in dcat_dataset_show
  dataset_dict = toolkit.get_action('package_show')(context, data_dict)
 File "/usr/lib/ckan/demo/src/ckan/ckan/logic/__init__.py", line 429, in wrapped
   result = _action(context, data_dict, **kw)
 File "/usr/lib/ckan/demo/src/ckan/ckan/logic/action/get.py", line 923, in package_show
    raise NotFound
NotFound