ASAN: Fix leak in KAStatsFavoritesModel

Summary:
Trace:
Direct leak of 336 byte(s) in 6 object(s) allocated from:
    #0 0x544cc0 in operator new(unsigned long) (/home/kfunk/devel/install/kf5/bin/plasmashell+0x544cc0)
    #1 0x7fbad15cddaf in KAStatsFavoritesModel::Private::entryForResource(QString const&) const /home/kfunk/devel/src/kf5/plasma-desktop/applets/kicker/plugin/kastatsfavoritesmodel.cpp:171:24
    #2 0x7fbad15b2d8e in KAStatsFavoritesModel::Private::addResult(QString const&, int, bool) /home/kfunk/devel/src/kf5/plasma-desktop/applets/kicker/plugin/kastatsfavoritesmodel.cpp:280:22
    #3 0x7fbad15b044f in KAStatsFavoritesModel::Private::Private(KAStatsFavoritesModel*, QString) /home/kfunk/devel/src/kf5/plasma-desktop/applets/kicker/plugin/kastatsfavoritesmodel.cpp:233:13
    #4 0x7fbad15a78ea in KAStatsFavoritesModel::initForClient(QString const&) /home/kfunk/devel/src/kf5/plasma-desktop/applets/kicker/plugin/kastatsfavoritesmodel.cpp:485:13
    ...

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D17039