Untangle cnt_error() entrance criteria:

We should never come in with a busyobj or obj.

Always allocate obj from Transient storage.

bin/varnishd/cache/cache_center.c

@@ -488,13 +488,10 @@ cnt_error(struct sess *sp, struct worker *wrk, struct req *req)
 	CHECK_OBJ_NOTNULL(wrk, WORKER_MAGIC);
 	CHECK_OBJ_NOTNULL(req, REQ_MAGIC);
 
-	if (req->obj == NULL) {
-		HSH_Prealloc(sp);
+	AZ(req->objcore);
+	AZ(req->obj);
 	AZ(wrk->busyobj);
 	wrk->busyobj = VBO_GetBusyObj(wrk);
-		req->obj = STV_NewObject(wrk, NULL, cache_param->http_resp_size,
-		     (uint16_t)cache_param->http_max_hdr);
-		if (req->obj == NULL)
 	req->obj = STV_NewObject(wrk, TRANSIENT_STORAGE,
 	    cache_param->http_resp_size,
 	    (uint16_t)cache_param->http_max_hdr);
@@ -506,14 +503,10 @@ cnt_error(struct sess *sp, struct worker *wrk, struct req *req)
 		sp->step = STP_DONE;
 		return(0);
 	}
-		AN(req->obj);
+	CHECK_OBJ_NOTNULL(req->obj, OBJECT_MAGIC);
 	req->obj->xid = req->xid;
 	req->obj->exp.entered = sp->t_req;
-	} else {
-		CHECK_OBJ_NOTNULL(wrk->busyobj, BUSYOBJ_MAGIC);
-		/* XXX: Null the headers ? */
-	}
-	CHECK_OBJ_NOTNULL(req->obj, OBJECT_MAGIC);
+
 	h = req->obj->http;
 
 	if (req->err_code < 100 || req->err_code > 999)