FIX: Properly close spectacle after Save As

Summary: BUG: 389694

Test Plan:

1. run Spectacle via shell
2. Have Quit after Save or Copy checked.
3. Hit Save As and save the image
4. Spectacle closes

Reviewers: davidre

Reviewed By: davidre

Subscribers: broulik, Spectacle

Tags: Spectacle

Differential Revision: https://phabricator.kde.org/D23534