Allow Package/Index file with an empty extension

When downloading Index files during an "update" operation there are
often "Index" files without an extension at all. So additionally to
"Index" extensions like: .gz, .lzma, .bz2 also try to download a
file/package without any filename extension.
What do you mean by string parsing in this situation?
I rather craft strings together than parsing them. But you are right: If someone intends to use the output of apt-offline for some other tools it would be better not to introduce the second of my patches.

I am sorry: I do not know how to handle this in github. I use mostly gerrit and if I create a second patch there they are two separate patches where the second just depends on the first.

So I hope you will apply the first one cause it improves the situation. The second patch in this branch/fork is just cosmetics.