Bug in content negotiation

[dgarijo]

Describe the bug
Content negotiation does not work.

To Reproduce
curl -sH "accept:application/rdf+xml" -L https://w3id.org/okn/i/mint/pihm-v4.1.0-baro-full
Error 400: SPARQL Query: No 'query=' parameter

Fuseki - version 3.8.0 (Build date: 2018-06-25T11:00:34+0000)

Expected behavior
Right content negotiation for ttl, XML and JSON-LD