Exiv2 fails to read metadata on images with duplicate tags

[Aerilius]

Some photos that have correct GPano tags do not trigger the panorama viewer.
This is because exiv2 fails to read any metadata if only some tags are inconsistent or duplicate. It seems duplicate tags are however common.

$ exiv2 -px example_duplicate_tags.jpg 
Error: XMP Toolkit error 203: Duplicate property or field node
Warning: Failed to decode XMP metadata.
example_duplicate_tags.jpg: (No XMP data found in the file)

example_duplicate_tags.jpg.zip

[Aerilius]

Probably have to revert commit 54b7f04 back to using exiftool. While exiv2 is used by many Gnome softwares, it's not in a default Ubuntu install, so we get a different but no extra dependency.