Visiting the file foo.tar below

    emacs -Q foo.tar

and trying to `tar-copy' the first entry to a file "zzz"

    C
    zzz

gets an error

    tar-copy: Args out of range: 513, 723

On a tar with a lot of files, the first of which is small, the command
succeeds, but the contents written are the text of the directory
listing, not the tar file.

I see tar-copy does a `widen' apparently to get at the data.  Does it
have to look in tar-data-buffer these days?