fix: keep file order

What

The file IDs are used in the order they are sent.

When using the IN operator, the database will return the files in the order they are stored on disk, which is usually the order they were inserted in. That explains why attachments were always ordered by file ID as noted in the issue.

To keep the advantage of having a single database query, I modified the query to add an order by clause instead of partly reverting 9f7cdb4b which would have meant multiple queries. This should keep any improved performance.

Why

fix #8647 (closed)