[Bug] Service report query do not return report if there are no binding in the service clause

[MaillPierre]

Issue Description:

The SPARQL service report is not computed if there is no result to the pattern in the service clause.

Expected Behavior:

Tested on a Corese server in sudo mode to authorize any SPARQL service in the query
First example query:

PREFIX js: <function://fr.inria.corese.core.extension.Report>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>

SELECT ?reportModeEndpointUrl ?_service_report_0 ?server WHERE {
  BIND( URI( CONCAT( STR(<http://fr.dbpedia.org/sparql>), "?mode=report" ) ) AS ?reportModeEndpointUrl)
  SERVICE ?reportModeEndpointUrl {
    ?s rdfs:label 'Banana'@en . 
  }
  values (?_service_report_0 ){
    (UNDEF )
  }
  BIND( js:server() AS ?server)
}

The results should be something like:

http://fr.dbpedia.org/sparql?mode=report, {...; server:Virtuoso, ...}; Virtuoso

Actual Behavior:

The example query returns no binding. Bindings are returned when the endpoint URL is passed from HTTP to HTTPS due to an SSL error. Testing on a local Fuseki server showed the same behavior. Even if there are no result corresponding to ?s rdfs:label 'Banana'@en . , an answer was received from the remote SPARQL endpoint and the report should be bound. The ?s variable does not appear in the result, so the fact that it is not bound is irrelevant.

Note to Developers:

Tested with Corese server 4.5.0.