Don't even try to create icons with empty sizes
Summary:
It's not enough to have QSize::isValid, as it needs both width and height
to be 0, so we explicitly check it.
Fixes a warning about writing into an empty image.
Reviewers: Frameworks, markg
Reviewed By: markg
Subscribers: markg, kfunk
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D5506