libarchive: open_zipped() does not need to check extensions for e.g. gzip

We only need to check for signature-less extensions,
currently only .lzma. The rest can be happily autodetected.

This fixes "zcat FILE_WITHOUT_GZ_EXT" case, among others.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
(cherry picked from commit 7c47b560a8fc97956dd8132bd7f1863d83c19866)
Signed-off-by: Mike Frysinger <vapier@gentoo.org>