If comment of the archive contains data which looks like
a zip64 directory, the comment is parsed as an
actual directory header.
Commit adds some additional checks similar to the checks
in minizip library.

Fixes #12449

Change-Id: Ia0fc950e47b9c39f77d88401b9ca30100ca7c808
Reviewed-on: https://go-review.googlesource.com/14433
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>