Fix mem leak found by ASAN

I found a mem leak with ASAN: Indirect leak of 48 byte(s) in 2 object(s) allocated from: #0 0x7f94067721af in operator new(unsigned long) (/usr/lib64/libasan.so.5+0x10c1af) #1 0x7f94048ae08e in KEditListWidgetPrivate::init(bool, QFlags<KEditListWidget::Button>, QWidget*) /compile/kde5/framework/frameworks/kwidgetsaddons/src/keditlistwidget.cpp:84 #2 0x7f94048aea16 in KEditListWidget::KEditListWidget(QWidget*) /compile/kde5/framework/frameworks/kwidgetsaddons/src/keditlistwidget.cpp:240 #3 0x7f940127ab72 in Ui_CachePolicyPage::setupUi(QWidget*) (/source5/kde/kde5.14/lib64/libKF5AkonadiWidgets.so.5+0x70b72)

The model was never deleted