More protection for SvTreeListBox.

Change-Id: I55731cd69aa12f5709e300759f556e29e8ceff5d
diff --git a/svtools/source/contnr/treelistbox.cxx b/svtools/source/contnr/treelistbox.cxx
index bc5e933e..1091438 100644
--- a/svtools/source/contnr/treelistbox.cxx
+++ b/svtools/source/contnr/treelistbox.cxx
@@ -2219,10 +2219,10 @@ void SvTreeListBox::GetFocus()

void SvTreeListBox::LoseFocus()
{
    //If there is no item in the tree, delete visual focus.
    if( !First())
    // If there is no item in the tree, delete visual focus.
    if ( !First() )
        Invalidate();
    if( pImp )
    if ( pImp )
        pImp->LoseFocus();
    Control::LoseFocus();
}
@@ -3514,6 +3514,8 @@ void SvTreeListBox::NotifyScrolled()

void SvTreeListBox::Invalidate( sal_uInt16 nInvalidateFlags )
{
    if (!pImp)
        return;
    if( nFocusWidth == -1 )
        // to make sure that the control doesn't show the wrong focus rectangle
        // after painting