[xmlsec] check for NULL - Coverity complains (Simo Sorce, Red Hat)

[Aleksey Sanin <aleksey src gnome org>]

commit c8769d391d33171bc8a2d819944eea163f872110
Author: Aleksey Sanin <aleksey aleksey com>
Date:   Wed Jun 4 09:24:00 2014 -0700

    check for NULL - Coverity complains (Simo Sorce, Red Hat)

 src/xmldsig.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/src/xmldsig.c b/src/xmldsig.c
index b452161..ad61042 100644
--- a/src/xmldsig.c
+++ b/src/xmldsig.c
@@ -789,7 +789,9 @@ xmlSecDSigCtxProcessSignedInfoNode(xmlSecDSigCtxPtr dsigCtx, xmlNodePtr node) {
     dsigCtx->signMethod->operation = dsigCtx->operation;
 
     /* calculate references */
-    cur = xmlSecGetNextElementNode(cur->next);
+    if(cur != NULL) {
+        cur = xmlSecGetNextElementNode(cur->next);
+    }
     while((cur != NULL) && (xmlSecCheckNodeName(cur, xmlSecNodeReference, xmlSecDSigNs))) {
         /* create reference */
         dsigRefCtx = xmlSecDSigReferenceCtxCreate(dsigCtx, xmlSecDSigReferenceOriginSignedInfo);