Bug 328296 DND of markers views causes NPE in StackRenderer
bundles/org.eclipse.e4.ui.workbench.renderers.swt/src/org/eclipse/e4/ui/workbench/renderers/swt/StackRenderer.java
int index = calcIndexFor(stack, element);
		cti = new CTabItem(ctf, createFlags, index);
		cti.setData(OWNING_ME, element);
		cti.setText(getLabel(part, part.getLabel()));
		cti.setImage(getImage(part));
		cti.setToolTipText(part.getTooltip());
		if (element.getWidget() != null) {
			
			
			Control ctrl = (Control) element.getWidget();
			if (ctrl.getParent() == ctf)
				cti.setControl((Control) element.getWidget());
		}
	}
	private int calcIndexFor(MElementContainer<MUIElement> stack,
			final MUIElement part) {
		int index = 0;
		
		for (MUIElement mPart : stack.getChildren()) {
			if (mPart == part)
				return index;
			if (mPart.isToBeRendered())
				index++;
		}
		return index;
	}
	@Override
	public void childRendered(
			final MElementContainer<MUIElement> parentElement,