Image files are added, but then Soundconverter complains when trying to encode them

[Pierre Equoy]

Version tested: 4.0.3
Ubuntu: 22.04

Steps to reproduce
==================

1. Prepare a folder with a few music files (*.flac), a text file (for instance blabla.cue) and at least one image file (for instance cover.jpg)
2. Drag and drop this folder into SoundConverter's main window

→ In the hamburger menu/Invalid Files entry, we can see that the cue file was rejected by gstreamer (OK)
→ The image file is added to the list along with the Flac files (Not OK!)

3. Start the conversion

→ When one of the encoding threads reaches the image file, a popup is shown and all encoding work is paused until the user presses OK to close the window

Expected outcome
================

- In 2, non-audio files are filtered out (even if gstreamer knows how to handle them, such as image files).
- In 3, an error that triggers a popup should not stop all workers from encoding the files they can encode. Instead of displaying a popup, it might be better to populate an error list and display it at the end?

This is annoying when trying to encode a big collection of albums. My use case is that I wanted to encode my music collection (albums ripped from my CD collection into Flac files) into Opus files. However, I cannot do that because it would mean too much manual work: Either I have to manually select the audio files and put them in SoundConverter (and make sure no image files are imported), either I have to stay in front of the GUI and press the "OK" button to close the popups.

[sezanzeb (sezanzeb)]

Has been fixed in 4.0.4: https://github.com/kassoulet/soundconverter/releases

[sezanzeb (sezanzeb)]

Available in ubuntu 23.10: https://packages.ubuntu.com/mantic/soundconverter