RAP - RDF API for PHP

In SparqlEngine.php function joinOptionalTuples, the initial logic testing
for one or more empty result sets seems wrong:

if(!$finalRes && !$res)
return array();

if(!$finalRes)
return $res;

if(!$res)
return $finalRes;

So for an optional join (where the optional results are passed in as
$finalRes), if there are no results from the left graph (in which case
there should be no optional results added), the entire optional result set
is instead returned.

Unless I'm misunderstanding something, this should read instead:

if(!$finalRes && !$res)
return array();

if(!$finalRes || !$res)
return $res;