restore: don't call free_mappings for an uninitialized list

    vma_area_list@entry=0x818) at criu/cr-dump.c:107
107             list_for_each_entry_safe(vma_area, p, &vma_area_list->h, list)
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

criu/cr-restore.c

@@ -3232,7 +3232,8 @@ static int sigreturn_restore(pid_t pid, struct task_restore_args *task_args, uns
 
 	if (current->parent == NULL) {
 		/* Wait when all tasks restored all files */
-		restore_wait_other_tasks();
+		if (restore_wait_other_tasks())
+			goto err_nv;
 	}
 
 	/*