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
* @see #setPageSize(Point)
     */
    public void setPageSize(int width, int height) {
        pageWidth = width;
        pageHeight = height;
    }
    /**
     * Sets the size of all pages.
     * The given size takes precedence over computed sizes.
     *
     * @param size the page size encoded as
     *   <code>new Point(width,height)</code>
     * @see #setPageSize(int,int)
     */
    public void setPageSize(Point size) {
        setPageSize(size.x, size.y);
    }
    /**
     * Sets the wizard this dialog is currently displaying.
     *
     * @param newWizard the wizard
     */
    protected void setWizard(IWizard newWizard) {
        wizard = newWizard;
        wizard.setContainer(this);
        if (!createdWizards.contains(wizard)) {
            createdWizards.add(wizard);
            
            nestedWizards.add(wizard);
            if (pageContainer != null) {