Double file extensions get mutated improperly

### Steps to reproduce

1. Enter a room that has a file saved with a double file extension such as `.tar.xz`
2. Press and hold on the screen until the popup menu comes up.
3. Press save
4. Check the name of the file downloaded

### Outcome

#### What did you expect?
The downloaded file's filename should have the intact `.tar.xz`
#### What happened instead?
The downloaded file's filename will look something like this: `my_file.tar_202405141906.xz`

### Your phone model

Google Pixel 8

### Operating system version

Android 14

### Application version and app store

1.6.14 [40106142] (F-310cecf5) F-Droid

### Homeserver

kde.org

### Will you send logs?

No

### Are you willing to provide a PR?

No