Upstream: avoid duplicate finalization. A request may be already finalized when ngx_http_upstream_finalize_request() is called, due to filter finalization: after filter finalization upstream can be finalized via ngx_http_upstream_cleanup(), either from ngx_http_terminate_request(), or because a new request was initiated to an upstream. Then the upstream code will see an error returned from the filter chain and will call the ngx_http_upstream_finalize_request() function again. To prevent corruption of various upstream data in this situation, make sure to do nothing but merely call ngx_http_finalize_request(). Prodded by Yichun Zhang, for details see the thread at http://nginx.org/pipermail/nginx-devel/2015-February/006539.html.