Otherwise package code would _only_ try to decrypt for salt and
iteration count present, which does not make sense for gpg.

Change-Id: Ie366f086a3c14d6b54b91b4edee8cfef1a42c44b
Reviewed-on: https://gerrit.libreoffice.org/47782Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Thorsten Behrens <Thorsten.Behrens@CIB.de>