[Bug]: Missing original filename in Preview's `Content-Disposition` header

[ShGKme]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github OR Nextcloud Community Forum (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Missing original filename in Preview's Content-Disposition header

Steps to reproduce

1. Open any Nextcloud page with an image preview (Viewer, Talk attachments)
2. Using the Web-Browser context menu download the image
3. Downloaded file is something like 683-1024.jpeg

Expected behavior

Content-Disposition header should include the original filename (possible with the size).

Nextcloud Server version

34 (master)