Prevent possible NULL pointer dereference.

cmd.c

 
 static void init_port_number(struct vcmd_param *p, struct port_set *port, const char *port_id) {
 	p->port_no = my_atoi(p->param);
+	if (!port) {
+		die("impossible! port == NULL");
+		return;
+	}
 	if (p->port_no == 0 || p->port_no > port->num) {
 		p->port_no = get_port_by_name(port, p->param);
 		if (!p->port_no)

display.c

 	struct videohub_commands *v = &videohub_commands[vcmd];
 	struct port_set *s_port = !v->ports1 ? NULL : (void *)d + v->ports1;
 	const char *p = v->opt_prefix;
+	if (!s_port)
+		return;
 	for(i = 0; i < s_port->num; i++) {
 		switch (v->type) {
 		case PARSE_LABEL: