avoid transcoding if device already has song(s)

[mikelpr]

• I have checked the FAQ for answers.
• I have checked the Changelog that the issue is not already fixed.
• I believe this issue is a bug, and not a general technical issue, question or feature requests that can be discussed on the forum.

Describe the bug
Currently, when copying to a device, if you have set Convert all music (trying this with an USB disk), Strawberry will transcode into its cache folder and then copy to the device. If you try to copy again a song, it will transcode again and then fail to copy.

To Reproduce

1. set Convert all music on file formats on a (storage) device properties
2. copy some songs to the device
3. copy them again

Expected behavior
Strawberry avoids transcoding songs that are already on the device

Screenshots:
(I don't think they're necessary but will provide if asked for)

System Information:

• Operating system: Fedora 40
• Strawberry Version: 1.0.23

Additional context
I believe Strawberry doesn't actually match the files on your library with those on the device - if you set it to "Do not convert any music" and try to copy files to device that are already there, it quickly fails for those that exist and shows the "Error copying songs" dialog listing them, with the log textbox below empty, where it probably just should not say anything since it's not really an error or just say that these files weren't copied since they already existed.

All being said, I think if "Overwrite existing files" is not checked and the file(s) exist it should totally skip the transcode step since it will fail on the copy step.