Catch and report API timeout

[merkys]

For some queries the server timeouts, but wdq dies with rather obscure message about failure to parse JSON. Failcase:

SELECT ?item ?smiles ?itemLabel
     WHERE { ?item wdt:P31 wd:Q11173 .
             ?item wdt:P233 ?smiles .
             SERVICE wikibase:label { bd:serviceParam wikibase:language "en". } }

It would be great if wdq could check for the HTTP return status (I believe server-side timeouts should set a proper one) and report it back to the user.