Fix GetItemRect to offset by the header window, if present.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@20546 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/listctrl.cpp

@@ -4914,6 +4914,8 @@ bool wxGenericListCtrl::SetItemData( long item, long data )
 bool wxGenericListCtrl::GetItemRect( long item, wxRect &rect,  int WXUNUSED(code) ) const
 {
     m_mainWin->GetItemRect( item, rect );
+    if ( m_mainWin->HasHeader() )
+        rect.y += HEADER_HEIGHT + 1;
     return TRUE;
 }