Should a page really be imported if it never was used by an `useImportedPage()` call?

[JanSlabon]

Actually following logic:

$pdf = new Fpdi();
$pdf->setSourceFile('template.pdf');
$pdf->importPage(1);
$pdf->AddPage();
$pdf->Output();

will copy the XObject of the imported page 1 and all of its resources to the resulting document. Though it was never used.
Can we add a check for this and do not import it at all then?