The saved_data variable in uv_loop_close() is only used when
NDEBUG is defined. This commit makes the variable declaration
depend on NDEBUG as well.
PR-URL: https://github.com/libuv/libuv/pull/1093
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>