qemu-nbd -l and -s options don't work together

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1810343
Reported by 'Michael' on 2019-01-02 :

When using qemu-nbd with -l to load a snapshot along with -s to create new
active layer the tool fails to find the snapshot specified on the command
line:

For example the following does not work:
  sudo qemu-nbd -s --load-snapshot=files  --connect /dev/nbd0 rootfs.qcow2
  Failed to load snapshot: Can't find snapshot

However, the following option works
  sudo qemu-nbd -s --connect /dev/nbd0 rootfs.qcow2
and so does
  sudo qemu-nbd --load-snapshot=files  --connect /dev/nbd0 rootfs.qcow2