Fix of cpu hog in event pipe. If client closed connection in ngx_event_pipe_write_to_downstream(), buffers in the "out" chain were lost. This caused cpu hog if all available buffers were in the "out" chain. Fix is to call ngx_chain_update_chains() before checking return code of output filter to avoid loosing buffers in the "out" chain. Note that this situation (all available buffers in the "out" chain) isn't normal, it should be prevented by busy buffers limit. Though right now it may happen with complex protocols like fastcgi. This should be addressed separately.

uwsgi_param  QUERY_STRING       $query_string;
uwsgi_param  REQUEST_METHOD     $request_method;
uwsgi_param  CONTENT_TYPE       $content_type;
uwsgi_param  CONTENT_LENGTH     $content_length;

uwsgi_param  REQUEST_URI        $request_uri;
uwsgi_param  PATH_INFO          $document_uri;
uwsgi_param  DOCUMENT_ROOT      $document_root;
uwsgi_param  SERVER_PROTOCOL    $server_protocol;

uwsgi_param  REMOTE_ADDR        $remote_addr;
uwsgi_param  REMOTE_PORT        $remote_port;
uwsgi_param  SERVER_PORT        $server_port;
uwsgi_param  SERVER_NAME        $server_name;