Fix for 'XMP Toolkit error 102: Composite nodes can't have values'

[JWCook]

Fix for the error:

XMP Toolkit error 102: Composite nodes can't have values

I narrowed this down to a file with Xmp.xmpMM.History with both a single value and an array (Xmp.xmpMM.History[1]). The array value was added by GIMP; not sure where the single value came from.

To fix this, and potentially the same issue with other tags, I added a check before writing XMP to remove any single-value keys if an array value also exists with the same key.

See also:

• https://github.com/drewnoakes/adobe-xmp-core/blob/1428bd60ed4ba7558f6511e4eca1dd18c23804c9/com/adobe/internal/xmp/impl/XMPMetaImpl.java#L1365-L1375
• https://kde-bugs-dist.kde.narkive.com/8HtjjDkX/bug-181853-new-entring-new-xmp-meta-data-removes-old-one-from-the-image-file