x059: Fix asymmetry in name constraints intersection

x059: Fix asymmetry in name constraints intersection

- In _gnutls_name_constraints_intersect, if *_nc had a node of some type not present in _nc2, this was preserved. However, if it was vice versa (_nc2 having a type not present in *_nc), this node was discarded.
- This is now fixed.
- Removed redundant return value check that was accidentally left when refactoring from set_datum to explicit NULL setting.

Signed-off-by: Martin Ukrop <mukrop@redhat.com>