s3:gencache: fix logic in stabilization when deleting a record from stable cache

s3:gencache: fix logic in stabilization when deleting a record from stable cache

Set state->written = true in the delete case
if and only if the record has really been deleted.

This does currently not seem to lead to an unneeded
write to the DB, since failure to delete the record
will cause the traverse and hence the transaction
to cancel. But I think this is clearer.

Signed-off-by: Michael Adam <obnox@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>