vcl PDF NSS sign: don't embed signed timestamp to the signature blob

There are several reasons to avoid doing so:

- The mscrypto backend doesn't do that, so the previous situation was
  inconsistent.
- PDF provides markup to provide a timestamp, and that's automatically
  part of the signed data.
- Page 10 of "PAdES Basic" specification from
  <http://www.etsi.org/deliver/etsi_ts%5C102700_102799%5C10277802%5C01.02.01_60%5Cts_10277802v010201p.pdf>
  explicitly requests either not writing that data, or writing it as an
  unsigned attribute (probably to underline that the value is from untrusted
  source, it's the signer's computer clock).

Change-Id: I35b1a9ef4a391a24e6695353d617f27c7d96d93b
Reviewed-on: https://gerrit.libreoffice.org/30926Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>

vcl/source/gdi/pdfwriter_impl.cxx

@@ -6621,7 +6621,7 @@ my_NSS_CMSSignerInfo_AddAuthAttr(NSSCMSSignerInfo *signerinfo, NSSCMSAttribute *
     return my_NSS_CMSAttributeArray_AddAttr(signerinfo->cmsg->poolp, &(signerinfo->authAttr), attr);
 }
 
-NSSCMSMessage *CreateCMSMessage(PRTime time,
+NSSCMSMessage *CreateCMSMessage(PRTime* time,
                                 NSSCMSSignedData **cms_sd,
                                 NSSCMSSignerInfo **cms_signer,
                                 CERTCertificate *cert,
@@ -6671,7 +6671,7 @@ NSSCMSMessage *CreateCMSMessage(PRTime time,
         return nullptr;
     }
 
-    if (NSS_CMSSignerInfo_AddSigningTime(*cms_signer, time) != SECSuccess)
+    if (time && NSS_CMSSignerInfo_AddSigningTime(*cms_signer, *time) != SECSuccess)
     {
         SAL_WARN("vcl.pdfwriter", "NSS_CMSSignerInfo_AddSigningTime failed");
         NSS_CMSSignedData_Destroy(*cms_sd);
@@ -6778,7 +6778,7 @@ bool PDFWriter::Sign(PDFSignContext& rContext)
     PRTime now = PR_Now();
     NSSCMSSignedData *cms_sd;
     NSSCMSSignerInfo *cms_signer;
-    NSSCMSMessage *cms_msg = CreateCMSMessage(now, &cms_sd, &cms_signer, cert, &digest);
+    NSSCMSMessage *cms_msg = CreateCMSMessage(nullptr, &cms_sd, &cms_signer, cert, &digest);
     if (!cms_msg)
         return false;
 
@@ -6803,7 +6803,7 @@ bool PDFWriter::Sign(PDFSignContext& rContext)
 
         NSSCMSSignedData *ts_cms_sd;
         NSSCMSSignerInfo *ts_cms_signer;
-        NSSCMSMessage *ts_cms_msg = CreateCMSMessage(now, &ts_cms_sd, &ts_cms_signer, cert, &digest);
+        NSSCMSMessage *ts_cms_msg = CreateCMSMessage(&now, &ts_cms_sd, &ts_cms_signer, cert, &digest);
         if (!ts_cms_msg)
         {
             free(pass);