Exit the program with an error when --add or --add-to are used without urls arguments

Summary: Without this, ark crashes with the same conditions.

Test Plan: ark --add --dialog

Reviewers: elvisangelaccio

Reviewed By: elvisangelaccio

Subscribers: kde-utils-devel, #ark

Tags: #ark

Differential Revision: https://phabricator.kde.org/D24912