[patch] SplitView causes script errors after being unloaded with Loader

After a SplitView is unloaded from a Loader, some signal handlers can still be called, causing script errors accessing the unloaded objects:

qtbase/qml/QtQuick/Controls/SplitView.qml:317: TypeError: Cannot read property 'length' of undefined

in updateLayout, called from:

item.Layout.maximumWidthChanged.connect(d.updateLayout)