dump: lazy-migration: don't try to cleanup zombie processes

The lazy memory dump used by the post copy migration cleans up page pipes
and parasite from zombie tasks, although for such task they are never
initialized.
Fix it.
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>

criu/cr-dump.c

@@ -1635,8 +1635,10 @@ static int cr_lazy_mem_dump(void)
 	ret = cr_page_server(false, true, -1);
 
 	for_each_pstree_item(item) {
-		destroy_page_pipe(dmpi(item)->mem_pp);
-		compel_cure_local(dmpi(item)->parasite_ctl);
+		if (item->pid->state != TASK_DEAD) {
+			destroy_page_pipe(dmpi(item)->mem_pp);
+			compel_cure_local(dmpi(item)->parasite_ctl);
+		}
 	}
 
 	if (ret)