Fix nullptr crash inXFA_FFBarcode::UpdateWidgetProperty().
Fix nullptr crash inXFA_FFBarcode::UpdateWidgetProperty().

BUG=chromium:655455

Review-Url: https://codereview.chromium.org/2421633002

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium