[master] 0c9897a An assert to guard against a problem spotted in 4.0

[Poul-Henning Kamp]

commit 0c9897a128a645c79cbaff5bfdd3c457f1ec691f
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Wed Mar 11 08:37:08 2015 +0000

    An assert to guard against a problem spotted in 4.0

diff --git a/bin/varnishd/http1/cache_http1_vfp.c b/bin/varnishd/http1/cache_http1_vfp.c
index 5c712bd..70e0e03 100644
--- a/bin/varnishd/http1/cache_http1_vfp.c
+++ b/bin/varnishd/http1/cache_http1_vfp.c
@@ -55,6 +55,7 @@ v1f_read(const struct vfp_ctx *vc, struct http_conn *htc, void *d, size_t len)
 
 	CHECK_OBJ_NOTNULL(vc, VFP_CTX_MAGIC);
 	CHECK_OBJ_NOTNULL(htc, HTTP_CONN_MAGIC);
+	assert(len >= 0);
 	l = 0;
 	p = d;
 	if (htc->pipeline_b) {