[zip]: Allow zip64 files to have prepended content.

This was already supported for non-zip64 files.

Fixed: 414848094
Change-Id: I3bd79f4b5175d8abca8d8e81f26373037868dcf8
Cq-Include-Trybots: luci.chromium.try:ios-blink-dbg-fyi
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6533087
Commit-Queue: Joshua Pawlicki <waffles@chromium.org>
Auto-Submit: Joshua Pawlicki <waffles@chromium.org>
Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1460236}
NOKEYCHECK=True
GitOrigin-RevId: 410a23e8a442e3de4f8df29339946a7d826120d0