File download Content-Type is application/octet-stream

[luya-bot]

This issue has originally been reported by @cebe at luyadev/luya-module-cms#85.
Moved here by @nadar.

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I uploaded a PDF file for download. Linking to that file presents the dowload as Content-Type: application/octet-stream which causes the browser to be unable to show it as PDF and will only save the download. Ideally serving the file with the correct content type would allow directly opening it as PDF.

Given that Type: pdf is already shown in the admin backend I assume the information is already available for serving the correct mime type.