If no slots were defined we try to allocate an empty bitmap, which
fails.
Signed-off-by: NDavid Hildenbrand <david@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Message-Id: <20180427120515.24067-1-david@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>