[rdf] Take first row from SPARQL results
[rdf] Take first row from SPARQL results

This prevents errors when a predicate has multiple properties, e.g.
http://nl.dbpedia.org/sparql?query=select+%2A+%7B%0A++++++++VALUES+%3Fs+%7B%3Chttp%3A%2F%2Fnl.dbpedia.org%2Fresource%2FWeimarrepubliek%3E%7DOPTIONAL+%7B%3Fs+%3Chttp%3A%2F%2Fdbpedia.org%2Fontology%2Fname%3E+%3F5%7D++%7D

driebit/ginger,driebit/ginger,driebit/ginger