Fix redirection of fd 0 in scripts sourced from interactive ash

Based on Busybox git 08d8b3cee1329d390f91bce419e2b4dadf484952 by
Denys Vlasenko <vda.linux@googlemail.com>.

Can be removed when we bump to 1.16.1 + patches or later

JL 03/06/10
Index: busybox-1.15.3/shell/ash.c
===================================================================
--- busybox-1.15.3.orig/shell/ash.c	2009-12-12 21:16:38.000000000 +0000
+++ busybox-1.15.3/shell/ash.c	2010-06-03 09:44:59.484647637 +0100
@@ -5071,7 +5071,7 @@
 		return 0;
 	pf = g_parsefile;
 	while (pf) {
-		if (fd == pf->fd) {
+		if (pf->fd > 0 && fd == pf->fd) {
 			return 1;
 		}
 		pf = pf->prev;