Issue when (eg.) removing Checksums-Sha256 fields are removed from .changes files

This bug was originally reported by Helmut Grohne (helmut@subdivi.de) in Debian bug #891867:

I'm working on adding more build profiles and diffoscope + reproducible
builds turn out to be an awesome tool in validating that my profiles
only drop packages and never change package contents. :)

Now I've run into a strange corner case with diffing .changes files. If
the last entry in a Checksums-Sha256 field is removed, new last entry is
removed and added. For example:

[snip]