[controls/BasicListItem] Fix binding loop introduced with reserveSpaceForSubtitle
The way this feature was implemented caused a binding loop:
file:///home/nate/kde/usr/lib64/qml/org/kde/kirigami.2/BasicListItem.qml:208:18: QML QQuickItem: Binding loop detected for property "implicitWidth"
file:///home/nate/kde/usr/lib64/qml/org/kde/kirigami.2/BasicListItem.qml:208:18: QML QQuickItem: Binding loop detected for property "implicitWidth"
There is a simpler way to implement this feature that avoids binding loops: when reserveSpaceForSubtitle: is set to true, simply always show the label item, even when it has no text.