Fixed ngx_http_test_reading() to finalize request properly.

Previous code called ngx_http_finalize_request() with rc = 0.  This is
ok if a response status was already set, but resulted in "000" being
logged if it wasn't.  In particular this happened with limit_req
if a connection was prematurely closed during limit_req delay.

src/http/ngx_http_request.c

@@ -2733,7 +2733,7 @@ closed:
     ngx_log_error(NGX_LOG_INFO, c->log, err,
                   "client prematurely closed connection");
 
-    ngx_http_finalize_request(r, 0);
+    ngx_http_finalize_request(r, NGX_HTTP_CLIENT_CLOSED_REQUEST);
 }