JunitTest_sc_unoapi crashed when accessing a disposed ScTextWnd from
~ScAccessibleEditLineTextData(), but the ScTextWnd::dispose() would also
call ScAccessibleEditLineTextData::Dispose() and clear mpWindow, so it
seems impossible to observe a disposed ScTextWnd in the dtor?

Change-Id: If571ee61d9a29601acb1de552ec1b9cc36d0d51e