Make ListBox handier post dispose.

Change-Id: I98fcf119a1a7118b46482a43c5f8acb7f0044900
diff --git a/vcl/source/control/lstbox.cxx b/vcl/source/control/lstbox.cxx
index 966ddbb..1cc42b1 100644
--- a/vcl/source/control/lstbox.cxx
+++ b/vcl/source/control/lstbox.cxx
@@ -521,9 +521,15 @@ vcl::Window* ListBox::GetPreferredKeyInputWindow()
void ListBox::LoseFocus()
{
    if( IsDropDownBox() )
        mpImplWin->HideFocus();
    {
        if (mpImplWin)
            mpImplWin->HideFocus();
    }
    else
        mpImplLB->HideFocus();
    {
        if (mpImplLB)
            mpImplLB->HideFocus();
    }

    Control::LoseFocus();
}