Download filename does not correspond to the name uploaded

### Steps to reproduce

1. Send an image named `菜.png` to myself.
2. On android, click on the image to enlarge it.
3. Click the download button.

### Outcome

#### What did you expect?

The downloaded filename should be called `菜_2022xxxxxxxxx.png`.

#### What happened instead?

The downloaded filename is actually `__2022xxxxxxxxx.png`.

Note that the filename is normal if I long-press the message and Save.

### Your phone model

pixel 4 xl

### Operating system version

android 11

### Application version and app store

1.4.14, f-droid

### Homeserver

not relevant

### Will you send logs?

No

### Are you willing to provide a PR?

No