Fix a crasher in ParsePostfixExpression()
Fix a crasher in ParsePostfixExpression()

BUG=pdfium:409
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1715363002 .

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