smbd: support breaking leases on an object where we don't have an own internal open

smbd: support breaking leases on an object where we don't have an own internal open

So far, when dealing with the rename destination, we had an internal open on
that which ensured get_existing_share_mode_lock() would always return a
lock.

Subsequently I'll want delay_for_handle_lease_break_send() to be callable on an
object that doesn't have a full internal open including locking.tdb entry, but
merely an open handle from filename_convert_dirfsp().

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15861

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Bjoern Jacke <bjacke@samba.org>