Certain failure scenarios, for instance PROXY protocol syntax errors,

are handled so fast that there may be no numerical difference between
the start and end session timestamps.

This is a consequence of our decision to use C type double (ieee 64bit FP)
for timestamps, at the current distance from POSIX epoch, 1.5 billion
seconds, the resolution is 238 nanoseconds.

bin/varnishd/cache/cache_session.c

@@ -560,7 +560,7 @@ SES_Delete(struct sess *sp, enum sess_close reason, double now)
 	if (reason == SC_NULL)
 		reason = (enum sess_close)-sp->fd;
 
-	assert(now > sp->t_open);
+	assert(now >= sp->t_open);
 	assert(VTAILQ_EMPTY(&sp->privs->privs));
 	VSL(SLT_SessClose, sp->vxid, "%s %.3f",
 	    sess_close_2str(reason, 0), now - sp->t_open);