This was broken since commit 9fe910e4
(xmlsecurity: use common NSS init in PDFDocument, 2016-10-13), after
that PDFDocument assumes that the client code does the crypto
initialization.

Change-Id: Iaee005afef6bd602c3a95e9a18f407c4d4223a26
Reviewed-on: https://gerrit.libreoffice.org/29887Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>