d67207fb CGNS Reader: Fix bad indexing when reading boundary conditions nodes

Acked-by: Kitware Robot <kwrobot@kitware.com>
Tested-by: buildbot <buildbot@kitware.com>
Reviewed-by: Julien Fausty <julien.fausty@kitware.com>
Reviewed-by: Thomas Galland <thomas.galland@kitware.com>
Merge-request: !10080