Accessibility Win: handle disabled state

[ChangeLog][QtGui] Windows Accessibility now handles the disabled state
of widgets correctly.

Task-number: QTBUG-36603

Change-Id: Ifebcf44320072089da66e81728de94e8f12a3354
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>

src/plugins/platforms/windows/accessible/qwindowsmsaaaccessible.cpp

@@ -1027,6 +1027,8 @@ HRESULT STDMETHODCALLTYPE QWindowsMsaaAccessible::get_accState(VARIANT varID, VA
         st |= STATE_SYSTEM_SIZEABLE;
     if (state.traversed)
         st |= STATE_SYSTEM_TRAVERSED;
+    if (state.disabled)
+        st |= STATE_SYSTEM_UNAVAILABLE;
 
     (*pvarState).vt = VT_I4;
     (*pvarState).lVal = st;