Bug 41927 [Dialogs] Selecting in PreferenceDialog generates too many invalid entries
20030825 If you select an entry, close the dialog and then reopen it selecting anotehr entry will result in a "this page has invalid values" although you selected nothing.
bundles/org.eclipse.jface/src/org/eclipse/jface/preference/PreferencePage.java
protected PreferencePage(String title) {
		super(title);
	}
	/**
	 * Creates a new abstract preference page with the given title and image.
	 *
	 * @param title the title of this preference page
	 * @param image the image for this preference page,
	 *  or <code>null</code> if none
	 */
	protected PreferencePage(String title, ImageDescriptor image) {
		super(title, image);
	}
	/**
	 * Computes the size for this page's UI control.
	 * <p>
	 * The default implementation of this <code>IPreferencePage</code>
	 * method returns the size set by <code>setSize</code>; if no size
	 * has been set, but the page has a UI control, the framework
	 * method <code>doComputeSize</code> is called to compute the size.
	 * </p>
	 *
	 * @return the size of the preference page encoded as
	 *   <code>new Point(width,height)</code>, or 
	 *   <code>(0,0)</code> if the page doesn't currently have any UI component
	 */
	public Point computeSize() {
		if (size != null)
			return size;
		Control control = getControl();