Never emit dataChanged signal when inserting new entries
dataChanged signal is for existing items. Hence, do not emit it when actually new items are added. Hopefully fixes the test failure after the shuffle playlist merge (https://build.kde.org/job/Applications/job/elisa/job/kf5-qt5%20FreeBSDQt5.13/), since the dataChanged signal was incorrectly emitted even before the endInsertRows signal was emitted when restoring entries.