vcl: add assert and improve lifecycle test.

Change-Id: Ic70a890dae41b04d6dd1f19cbea419fe5a794af3

vcl/qa/cppunit/lifecycle.cxx

@@ -90,6 +90,7 @@ void LifecycleTest::testParentedWidgets()
     VclPtr<WorkWindow> xWin(new WorkWindow((vcl::Window *)NULL,
                                                  WB_APP|WB_STDWORK));
     CPPUNIT_ASSERT(xWin.get() != NULL);
+    xWin->Show();
     testWidgets(xWin);
 }
 

vcl/source/window/window.cxx

@@ -144,6 +144,10 @@ void Window::dispose()
     assert( !mpWindowImpl->mbInDispose && "vcl::Window - already in dispose()" );
     mpWindowImpl->mbInDispose = true;
 
+    assert( !mpWindowImpl->mpParent ||
+            !mpWindowImpl->mpParent->IsDisposed() ||
+            "vcl::Window child should have its parent disposed first" );
+
     // remove Key and Mouse events issued by Application::PostKey/MouseEvent
     Application::RemoveMouseAndKeyEvents( this );