to handle the unlikely case of `ns` being deeper than `remote-ns`,
`max-depth` being set to `None` and a too-deep sub-ns of `ns` existing.
such a sub-ns cannot have been created by a previous run of this sync
job, so avoid unexpectedly removing it.
Signed-off-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>