set request handlers, this fixes complex proxied 400 handler with SSI includes

src/http/ngx_http_request.c

@@ -1751,6 +1751,9 @@ ngx_http_finalize_request(ngx_http_request_t *r, ngx_int_t rc)
             }
         }
 
+        c->read->handler = ngx_http_request_handler;
+        c->write->handler = ngx_http_request_handler;
+
         ngx_http_finalize_request(r, ngx_http_special_response_handler(r, rc));
         return;
     }