Where there is no package description, show a blank line.

This is the correct behaviour where a package description
isn't supplied, and it fixes (a) cause of issue #104, although
there are others. However, it can also serve to hide
the situation with split packages, which are going to be a bigger
headache in themselves!
Merge pull request #124 from nc6/fixes/pkgdesc_missing

Where there is no package description, show a blank line.