Bug 303549 [UI] Dragging the last element from a stack causes placeholders to appear
The check to 'pick' a new element to select isn't checking whether the 'toBeRendered' is true.
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/workbench/ui/renderers/swt/StackRenderer.java
public StackRenderer() {
		super();
	}
	@PostConstruct
	public void init() {
		super.init(eventBroker);
		itemUpdater = new EventHandler() {
			public void handleEvent(Event event) {
				Object objElement = event
						.getProperty(UIEvents.EventTags.ELEMENT);
				
				if (!(objElement instanceof MUILabel)
						|| !(objElement instanceof MUIElement))
					return;
				
				MUIElement uiElement = (MUIElement) objElement;
				MUILabel modelItem = (MUILabel) objElement;
				
				MElementContainer<MUIElement> parent = uiElement.getParent();
				if (!(parent.getRenderer() == StackRenderer.this))
					return;
				
				MElementContainer<MUIElement> stack = uiElement.getParent();
				CTabItem item = findItemForPart(stack, uiElement);
				if (item == null)
					return;
				String attName = (String) event
						.getProperty(UIEvents.EventTags.ATTNAME);
				if (UIEvents.UILabel.LABEL.equals(attName)) {
					String newName = (String) event