Bug 182190 [StatusHandling] [Wizards] getControl assert on wizard page has no message
M6 If you forget to set the control on your wizard page our assert gives no feedback. We need an error message.
bundles/org.eclipse.jface/src/org/eclipse/jface/wizard/WizardDialog.java
private Button helpButton;
    private SelectionAdapter cancelListener;
    private boolean isMovingToPreviousPage = false;
    private Composite pageContainer;
    private PageContainerFillLayout pageContainerLayout = new PageContainerFillLayout(
            5, 5, 300, 225);
    private int pageWidth = SWT.DEFAULT;
    private int pageHeight = SWT.DEFAULT;
    private static final String FOCUS_CONTROL = "focusControl"; 
    private boolean lockedUI = false;
	
    private ListenerList pageChangedListeners = new ListenerList();
    
    private ListenerList pageChangingListeners = new ListenerList();
    /**
     * A layout for a container which includes several pages, like
     * a notebook, wizard, or preference dialog. The size computed by
     * this layout is the maximum width and height of all pages currently
     * inserted into the container.
     */
    protected class PageContainerFillLayout extends Layout {
        /**
         * The margin width; <code>5</code> pixels by default.
         */
        public int marginWidth = 5;
        /**
         * The margin height; <code>5</code> pixels by default.
         */
        public int marginHeight = 5;
        /**