function TCustomListBox.ItemAtPos(const Pos: TPoint; Existing: Boolean
  ): Integer;
begin
  Result := GetIndexAtXY(Pos.X, Pos.Y);
  if Existing then
  begin
    if Result >= Items.Count then
      Result := -1;
  end else
  begin
    if (Result < 0) and (Result > Items.Count) and PtInRect(ClientRect, Pos) then
      Result := Items.Count;
  end;
end; 

procedure TMyListBox.Click;
var
  P: TPoint;
  I: Integer;
  R: TRect;
begin
  P := ScreenToClient(Mouse.CursorPos);
  I := ItemAtPos(P, True);

  if I < 0 then
    Exit;

  R := ItemRect(I);
  if not R.Contains(P) then
    Exit;

  //inherited Click;  

procedure TCustomListBox.LMSelChange(var TheMessage);
begin
  if [csLoading,csDestroying,csDesigning]*ComponentState<>[] then exit;
  DoSelectionChange(FLockSelectionChange = 0);
end;