PNG nonconformance: duplicate eXIf chunks.

[jbowler]

I'm seeing files produced in November 2024 and later and apparently originally authored by PhotoShop 2024 and/or LightRoom which have the same eXIf chunk duplicated both before and after IDAT. This may have been fixed by the change in July 2023 which, so far as I can determine, prevents are write after IDAT if you occurred before and, anyway, I didn't think PhotoShop used libpng.

This issue is a placeholder in case anyone else sees it. libpng appears to be correct and it looks like the bug was fixed in July 2023