message: fix(pkgid): fallback when `host` does not exist
diff: @@ -279,7 +279,8 @@ impl fmt::Display for PackageIdSpec {
  match self.url {
  Some(ref url) => {
  if url.scheme() == "cargo" {
  - write!(f, "{}{}", url.host().unwrap(), url.path())?;
  + let host = url.host().unwrap_or(url::Host::Domain(""));
  + write!(f, "{}{}", host, url.path())?;
  } else {
  write!(f, "{}", url)?;
  }
  