Attachment viewer shows attachment ID instead of file name in title

[ChristophWurst]

Steps to reproduce

1. Open a message with PDF attachments
2. Click on one of the attachments
3. Look at the title (above the PDF viewer)

Expected behavior

I see the name of the attachment, e.g. presentation.pdf.

Actual behavior

I see 2, 3 or whatever body part ID the attachment has. That is because Viewer splits the route into directory and basename. And with our attachment URL the basename is the ID.

Mail app version

2.0.0 beta 3

Mailserver or service

No response

Operating system

No response

PHP engine version

No response

Web server

No response

Database

No response

Additional info

No response