Fixes #585: ESI produces wrong backend requests.

$OpenBSD: patch-bin_varnishd_cache_vrt_esi_c,v 1.1 2009/12/12 17:38:19 fgsch Exp $
--- bin/varnishd/cache_vrt_esi.c.orig	Sat Dec 12 16:20:24 2009
+++ bin/varnishd/cache_vrt_esi.c	Sat Dec 12 16:20:39 2009
@@ -384,7 +384,7 @@ esi_handle_include(struct esi_work *ew)
 			memcpy(c, val.b, Tlen(val));
 			val.b = c;
 			val.e = val.b + s;
-			*val.e = '\0';
+			val.e[-1] = '\0';
 		}
 
 		if (Tlen(val) > 7 && !memcmp(val.b, "http://", 7)) {
