networkd: make sure we allocate the NTA set before we add items to it

See: #2683

src/network/networkd-network.c

@@ -994,6 +994,10 @@ int config_parse_dnssec_negative_trust_anchors(
                         continue;
                 }
 
+                r = set_ensure_allocated(&n->dnssec_negative_trust_anchors, &dns_name_hash_ops);
+                if (r < 0)
+                        return log_oom();
+
                 r = set_put(n->dnssec_negative_trust_anchors, w);
                 if (r < 0)
                         return log_oom();