Fix counting up placeholder (%Nd)

Summary: The change from QString to Qurl in 0a1f081ebe75eaf25a1142e5efd00cb2354e35fe broke it.

Test Plan: Press save button two times

Reviewers: Spectacle, broulik

Reviewed By: broulik

Subscribers: broulik

Tags: Spectacle

Differential Revision: https://phabricator.kde.org/D22113