Ticket 50741-cont bdb_start - Detected Disorderly Shutdown
Bug: Offline import does no longer write guardian file, next
normal start will raise a Disorderly Shutdown
Fix: The bug was introduced with the fix for #50659 when dblayer_close() was
removed from import_moain_offline becasue it was called twice in some
scenarios. But it did miss in ldif2db. Add it there.
Also correct function reference in error messages
Reviewed by: Thierry, thanks