Fixed 'Too many open statements' error for Iterator-based finder methods...

This commit complements e6fde53:develop/6 in openlink/virtuoso-opensource.

When closing an ```Iterator``` used for finding triples, its corresponding Java SQL ```ResultSet``` is also closed, but not the SQL ```Statement``` that the ```ResultSet``` belongs to. If many finder queries are used, a 'Too many open statements' is thrown by Virtuoso, even when correctly closing ```Iterator```s.

This should also be merged into develop/7.