generate_repository: fixes always re-downloading packages.
generate_repository: fixes always re-downloading packages.

The package_name variable is a relative path to the download_dir, hence
why we need to be in the download_dir to correctly determine if the package
exists already.

Signed-off-by: Chris Lapa <711c73f64afdce07b7e38039a96d2224209e9a6c@lapa.com.au>

GusBricker/fancy-sauce