Handle Zip archives that are "multi-part archives with only
one part" by simply ignoring the marker at the beginning
of the file. (Zip archivers reserve four bytes at the beginning
of each part of a multi-part archive, if it happens to only
require one part, those four bytes get filled with a placeholder
that can be ignored.)

Thanks to: Marius Nuennerich,

	 for pointing me to a Zip archive that libarchive couldn't handle

MFC after: 7 days