handle zip files embedded within zip files

Summary:
if we need to fetch the sizes from a PK78 header, there might be a PK34 header before it if there is a zip file embedded (e. g. an epub within a zip).

BUG: 73821
FIXED-IN: 5.47

Test Plan: autotest in a separate commit

Reviewers: dfaure, Frameworks

Reviewed By: dfaure

Subscribers: ngraham, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D11155