Our public free functions explicitly don't accept NULL pointers
(sigh). Therefore, callers must do something like this:
if (dev)
virNodeDeviceFree(dev);
And we are not doing that on two places I've found. This leads to
dummy error message thrown by virsh:
virsh # nodedev-dumpxml nonexistent-device
error: Could not find matching device 'nonexistent-device'
error: invalid node device pointer in virNodeDeviceFree
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>