Change hwloc_get_child/obj_covering_cpuset() to return NULL when the given cpuset is empty. Otherwise, we'd return the very first PROC, which would be very strange.
Change hwloc_get_child/obj_covering_cpuset() to return NULL
when the given cpuset is empty. Otherwise, we'd return
the very first PROC, which would be very strange.

git-svn-id: 14be032f8f42541b1a281b51ae8ea69814daf20e@1301 4b44e086-7f34-40ce-a3bd-00e031736276

BlueBrain/hwloc,BlueBrain/hwloc,BlueBrain/hwloc,BlueBrain/hwloc