Compression errors

[M-Gonzalo]

I've been doing a little light testing on undup (can't believe this isn't more known, BTW, it's very good). But I'm finding some errors very frequently:

und_check: size mismatch at #######

####### being different positions, of course, depending on the particular stream.

I'm testing on Manjaro Linux 5.14, up to date. Don't hesitate to reach out if you need more testing done. I also have access to an ARM box