Fails (silently) if deb package uses zstd

[sevens]

Using deb2tgz on a Debian package that uses zstd for its internal compression (e.g. data.tar.zst) fails silently: no Slackware package is created and no output is generated.

To reproduce:

• Download a Debian package that uses zst (any package for a recent Ubuntu release should do, e.g. https://packages.ubuntu.com/jammy/amd64/less/download )
• Try to convert it using deb2tgz
• Observe that no Slackware package is created

[sevens]

I've added a quick fix ( sevens@9a99096 and sevens@9829fbf ), can create a pull request for it if you want.

[vborrego]

Hi @sevens . Made a correction based on your suggested commits regarding zst.

[sevens]

Nice, thanks :)

FYI: I also made 2 other small changes/improvements which might be useful:

• Exit with error on unsupported compression formats (sevens@a0313ae), should make it much easier to debug/troubleshoot similar problems in the future
• Output error messages to stderr (sevens@3d9cab1)

Let me know if a pull request for any of these is desired.