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