cubicweb-datacat #5511214 DCAT RDF data import crash if URI is not RDF. [validation pending]

We can find malformed RDF data like this:

<dset_uri> a dcat:Dataset ;
    dcat:distribution <http://example.org/file.pdf>

The distribution URI should have been RDF data, instead it's a PDF file download URL.

In such cases, the data import process crash with a rdflib.PluginException error. Instead it should ignore such URIs/URLs.

priorityimportant
typebug
done in0.3.0
load left0.000
closed by#b0ca2755c135 Catch new exception when importing DCAT RDF data.
patchCatch new exception when importing DCAT RDF data. [applied]