Add triples only if they are not stoppped at

* update test

GraphExtract should updates its model _after_ it is checked if the triple should be taken into account or stopped at (ok, it's maybe not really a bug , depending on your your definition if "stop at" is meant inclusive or exclusive).

As reflected in the test, this prohibits the creation of a dangling pointer (that is: a bnode in object position while the creation of a bnode resource is prevented by TripleBoundary.stopAtAnonObject )).