If realize fails, domains and endpoints trees may be NULL. On
unrealize(), this produces assertions:

"GLib: g_tree_destroy: assertion 'tree != NULL' failed"

Check that the trees are non NULL before destroying them.

Cc: qemu-stable@nongnu.org
Signed-off-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>

Message-Id: <20200908193309.20569-2-eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>