Blender Git Loki

Definitely remove the exception safety code.

It was first included as a safety net, but after close inspection of
where exceptions are used in the OpenVDB library, it appears that about
half of them are not used at all whilst the others are fairly dumb and
can be avoided gracefully (e.g. openvdb::ValueError is thrown in some
place if a negative value is passed, so don't pass a negative value ;).

Also the only place where it was used could hardly result in an
exception (only happens if the file is not a .vdb file, so let's trust
the user on that).