[master] 1ebd861 grace=0 should not mean "use default"

[Poul-Henning Kamp]

commit 1ebd86156a21a62bda61059958a3a0146e78bb1f
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Fri Mar 11 14:15:10 2011 +0000

    grace=0 should not mean "use default"
    
    Spotted by:	Geoff

diff --git a/bin/varnishd/cache_expire.c b/bin/varnishd/cache_expire.c
index c95c43f..3a691a6 100644
--- a/bin/varnishd/cache_expire.c
+++ b/bin/varnishd/cache_expire.c
@@ -119,7 +119,7 @@ EXP_Grace(const struct sess *sp, const struct object *o)
 	double r;
 
 	r = (double)params->default_grace;
-	if (o->exp.grace > 0.)
+	if (o->exp.grace >= 0.)
 		r = o->exp.grace;
 	if (sp != NULL && sp->exp.grace > 0. && sp->exp.grace < r)
 		r = sp->exp.grace;