listview: appending item when highlight moving will result in not visible highlight

if the currentitem is the last visible item, then down keyevent will result in currentIndex ++, and then highlight moving follow currentItem, the listview will track the highlight.

but if we append item when highlight moving, the model changed (may be applyModelChanges) will set moveReason = QQuickItemViewPrivate::Other; and it will result in 'trackedPositionChanged' no effect.

then the listview stop tracking highlight, we can only see part of highlight even no highlight after that.