lvmlockd: fix vgchange --locktype sanlock

lvmlockd: fix vgchange --locktype sanlock

Fix regression from commit 7f29afdb06d
"lvmlockd: configurable sanlock lease sizes on 4K disks"

That change failed to recognize that a running lockspace will not
exist in lvmlockd when converting a local VG to a sanlock VG, i.e.
vgchange --locktype sanlock vgname.  When the vgchange attempted
to initialize new lv leases for existing LVs, lvmlockd would
return an error when it found no lockspace.