It is possible for 'mdevctl' to output nothing, an empty string
(e.g. when no mediated devices are defined on the host). What is
weird is that when passing '--defined' then 'mdevctl' outputs an
empty JSON array instead. Nevertheless, we should accept both and
treat them the same, i.e. as no mediated devices.
Resolves: https://gitlab.com/libvirt/libvirt/-/issues/523 Signed-off-by: Michal Privoznik <mprivozn@redhat.com> Reviewed-by: Kristina Hanicova <khanicov@redhat.com>