seccomp: Fix typo in collect_filters

*** CID 190178:  Null pointer dereferences  (NULL_RETURNS)
/criu/seccomp.c: 296 in collect_filters()
Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/seccomp.c

@@ -287,7 +287,7 @@ static int collect_filters(struct pstree_item *item)
 
 	for (i = 0; i < item->nr_threads; i++) {
 		entry = seccomp_find_entry(item->threads[i].real);
-		if (!leader) {
+		if (!entry) {
 			pr_err("Can't collect filter on tid_real %d\n",
 			       item->pid->real);
 			return -1;