Bug#886750: build fails on mystery missing file "devel"

[Hans-Christoph Steiner]

Package: cowbuilder
Version: 0.73

Sometimes I forget and try to build a .changes file rather than the .dsc
file.  cowbuilder then fails with a mystery missing file called "devel":

I: copying [/code/collab-maint/fdroidserver_1.0.0-1~bpo9+1_source.changes]
I: copying [/code/collab-maint/devel]
cp: cannot stat '/code/collab-maint/devel': No such file or directory

Apparently this is because .changes and .dsc have different column
counts.  The "devel" comes from entries like this:

Files:
053ebf50900ddd97d4310d167604f22c 1457 devel optional
fdroidserver_1.0.0-1.dsc


.hc