Track split ZIP corrupts filenames containing special characters #552

When downloading multiple split TAF tracks as a ZIP archive, filenames containing special characters are corrupted inside the ZIP.

This can be reproduced with track titles containing typographic quotation marks such as „ and ”.

For example, the track title:

09 3. Satz: „Allegro”

is shown correctly in the TeddyCloud Web UI, but the resulting filename inside the downloaded ZIP becomes:

09 3. Satz: ÔÇ×AllegroÔÇ£.ogg

The same happens for the other affected tracks.

Steps to reproduce

1. Open a TAF containing track titles with special characters, e.g. typographic quotation marks.
2. Open the track download / split dialog.
3. Select multiple tracks so that TeddyCloud creates a ZIP archive.
4. Download the ZIP.
5. Open the ZIP, e.g. with Windows Explorer.

Expected behavior

The filenames inside the ZIP should preserve the original UTF-8 track titles, e.g.:

09 3. Satz: „Allegro”.ogg

Actual behavior

The UTF-8 characters are interpreted using the wrong character encoding:

09 3. Satz: ÔÇ×AllegroÔÇ£.ogg

Additional information

The track titles are displayed correctly in the Web UI, so the problem appears to occur when TeddyCloud creates the ZIP entries for the split tracks.

This looks like a ZIP filename encoding issue, e.g. the filenames being UTF-8 encoded without the corresponding UTF-8 filename flag / metadata being set in the ZIP archive.

The audio files themselves are downloaded correctly; only the filenames inside the ZIP are affected.