pstree: initialize real pid to -1 for threads on restore

We are going to check is it valid or not.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

pstree.c

@@ -363,8 +363,10 @@ static int read_pstree_image(void)
 		if (!pi->threads)
 			break;
 
-		for (i = 0; i < e->n_threads; i++)
+		for (i = 0; i < e->n_threads; i++) {
+			pi->threads[i].real = -1;
 			pi->threads[i].virt = e->threads[i];
+		}
 
 		task_entries->nr_threads += e->n_threads;
 		task_entries->nr_tasks++;