conf: Alter when ctxt->node is set

In virDomainMemoryDefParseXML and virDomainVideoDefParseXML if
the VIR_ALLOC fails and NULL is returned, then the alteration
to ctxt->node isn't reversed.

Found by Coverity
Signed-off-by: NJohn Ferlan <jferlan@redhat.com>
Reviewed-by: NErik Skultety <eskultet@redhat.com>

src/conf/domain_conf.c

@@ -15089,11 +15089,11 @@ virDomainVideoDefParseXML(virDomainXMLOptionPtr xmlopt,
     char *vgamem = NULL;
     char *primary = NULL;
 
-    ctxt->node = node;
-
     if (!(def = virDomainVideoDefNew()))
         return NULL;
 
+    ctxt->node = node;
+
     cur = node->children;
     while (cur != NULL) {
         if (cur->type == XML_ELEMENT_NODE) {
@@ -15830,11 +15830,11 @@ virDomainMemoryDefParseXML(virDomainXMLOptionPtr xmlopt,
     virDomainMemoryDefPtr def;
     int val;
 
-    ctxt->node = memdevNode;
-
     if (VIR_ALLOC(def) < 0)
         return NULL;
 
+    ctxt->node = memdevNode;
+
     if (!(tmp = virXMLPropString(memdevNode, "model"))) {
         virReportError(VIR_ERR_XML_ERROR, "%s",
                        _("missing memory model"));