For some reason I couldn't entirely get behind, `changedEntries` was signalled to change on the QML side on component creation.
Even when replacing the `Binding` by a direct binding, this wouldn't work. However, while I can't just `alias` it, it turns out, `ghnsDialog` already has a `changedEntries` alias, which we can then just bind to.
Furthermore, don't signal a change when clearing if it was already empty.
This fixes the wallpaper model in Plasma reloading in-flight, causing thumbnail generation to fail. While this is a genuine bug in the model it only started to be a problem with GHNS needlessly reloading the model.
BUG: 419234