Bug fix: incorrect oldValue in InputFieldInitializer

[happyhua]

When setValue (with either silent = true or false) is called on a formElement, the oldValue in InputFieldInitializer is not updated correctly. This can later lead to an incorrect oldValue being passed to formElement.triggerChangeListeners.

        TextBox box = new TextBox();

        box.withValue("Start");

        box.addChangeListener((oldValue, newValue) -> {
            // Expected oldValue is "Start", but the current code returns null/empty.
            DomGlobal.console.log(oldValue + ", " + newValue);
        });

        Domino.body().appendChild(box);