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.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
assertEquals(partA, stack.getSelectedElement());
	}
	public void testPart_ToBeRendered2() throws Exception {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		application.setContext(appContext);
		appContext.set(MApplication.class.getName(), application);
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
		window.getChildren().add(stack);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		partA.setElementId("partA");
		partA.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partB.setElementId("partB");
		partB.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.workbench.SampleView");
		partB.setToBeRendered(false);
		stack.getChildren().add(partA);
		stack.getChildren().add(partB);
		stack.setSelectedElement(partA);
		wb = new E4Workbench(application, appContext);
		wb.createAndRunUI(window);
		CTabFolder tabFolder = (CTabFolder) stack.getWidget();
		assertEquals(1, tabFolder.getItemCount());
		assertEquals(0, tabFolder.getSelectionIndex());
		partB.setToBeRendered(true);
		assertEquals(
				"Rendering another part in the stack should not change the selection",
				0, tabFolder.getSelectionIndex());