--save flag is ignored if file is already signed

[BoostCookie]

How to reproduce:

sbctl sign myfile.efi
sbctl list-files  # as expected file is not in the database
sbctl sign -s myfile.efi  # run command again with -s flag to save it to the database
sbctl list-files  # the file is still not in the database

I think this error was introduced with 638fd00

[SorenHJohansen]

It seems like that func Sign should only return early if signing fails with a real error (not just “already signed”):

if err != nil && !errors.Is(err, ErrAlreadySigned) {
            return err
        }

Maybe also to improve user feedback, consider handling the ErrAlreadySigned case explicitly in SignCmd:

switch {
	case errors.Is(err, sbctl.ErrAlreadySigned):
			if save {
				logging.Print("File has already been signed. Files were saved %s\n", output)
			} else {
				logging.Print("File has already been signed %s\n", output)
			}
			return nil

[BoostCookie]

That first suggestion is pretty much what my Pull Request does. Did you mean to comment there?