Make a valid pkgsummary entry for an "invalid" pkg

This is blocking external processes from getting updates to piuparts package status.

pkgsummary was assuming that package entries would never be made with an "invalid" state. In that case, the entry would end up with the default url "invalid url", which never should be the result. When an actual package with an "invalid" state is entered, the eventual global summary creation will fail on the bad url. Fix by always replacing a default entry.

Test included.