don't leave current item index invalid after SetItemCount() (ticket #3720)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_8_BRANCH@53998 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/vlbox.cpp

@@ -98,6 +98,10 @@ wxVListBox::~wxVListBox()
 
 void wxVListBox::SetItemCount(size_t count)
 {
+    // don't leave the current index invalid
+    if ( m_current != wxNOT_FOUND && (size_t)m_current >= count )
+        m_current = count - 1; // also ok when count == 0 as wxNOT_FOUND == -1
+
     if ( m_selStore )
     {
         // tell the selection store that our number of items has changed