Comment 7 for bug 1663695

I just wanted to reject that assumption because the version of AppStream in Xenial was too old, but it turns out you're right: A backport from a newer version broke this, and I didn't notice because my AppStreamQt is also newer (and using a better architecture where this bug can't happen anymore).
So, +1 on the patch. I would probably when we are patching this, also add a few minor fixes to the autopkgtests in Xenial (I might do that tomorrow).