SQUASHME: fix incorrect assertion

The expectation that withdrawing would drop the last reference was
inferred from the assertion on having the sole reference a few lines
above. Except that we grant up to one request a reference to the oc
before we rush it.

bin/varnishd/cache/cache_hash.c

@@ -955,8 +955,8 @@ HSH_Withdraw(struct worker *wrk, struct objcore **ocp)
 	assert(oc->refcnt == 1);
 	assert(oh->refcnt > 0);
 	oc->flags = OC_F_WITHDRAWN;
-	hsh_rush1(wrk, oc, &rush);
-	AZ(HSH_DerefObjCoreUnlock(wrk, &oc));
+	hsh_rush1(wrk, oc, &rush); /* grabs up to 1 oc ref */
+	assert(HSH_DerefObjCoreUnlock(wrk, &oc) <= 1);
 
 	hsh_rush2(wrk, &rush);