Fix crash in DHCPv6 information-request handler.

src/rfc3315.c

@@ -1027,7 +1027,7 @@ static int dhcp6_no_relay(int msg_type, struct in6_addr *link_address, struct dh
       {
 	/* We can't discriminate contexts based on address, as we don't know it.
 	   If there is only one possible context, we can use its tags */
-	if (context && !context->current)
+	if (context && context->netid.net && !context->current)
 	  {
 	    context->netid.next = NULL;
 	    context_tags =  &context->netid;