Bug 331685 Unset context from model if widget creation failed since the context is disposed
If the renderer fails to create a widget for a given element, it will dispose its created context (if any) prior to returning from the call. If we try to deconstruct the element later, it will fail with an NPE because the context has been disposed and getParent() will return null.
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
protected IEventBroker eventBroker;
	@Inject
	EModelService modelService;
	@Inject
	protected Logger logger;
	private Shell limbo;
	private List<MUIElement> renderedElements = new ArrayList<MUIElement>();
	private MUIElement removeRoot = null;
	@Inject
	public PartRenderingEngine(
			@Named(E4Workbench.RENDERER_FACTORY_URI) @Optional String factoryUrl) {
		if (factoryUrl == null) {
			factoryUrl = defaultFactoryUrl;
		}
		this.factoryUrl = factoryUrl;
	}
	protected void fixZOrder(MUIElement element) {
		MElementContainer<MUIElement> parent = element.getParent();
		if (parent == null || !(element.getWidget() instanceof Control))
			return;
		Control elementCtrl = (Control) element.getWidget();
		Control prevCtrl = null;
		for (MUIElement kid : parent.getChildren()) {
			if (kid == element) {
				if (prevCtrl != null)
					elementCtrl.moveBelow(prevCtrl);
				else
					elementCtrl.moveAbove(null);
				return;
			} else if (kid.getWidget() instanceof Control) {