QItemDelegate::doLayout added a margin after the checkbox which is not
done within QCommonStylePrivate::viewItemLayout. This created a small
but visual difference between using QItemDelegate or QStyledItemDelegate.
The additional margin was removed from viewItemLayout somehwere between
4.4 and 4.5 so it was intentional.
Change-Id: I2fc3f287fe8b181355edeebec9626c49d85fe74d
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>