Optimize code for example

Signed-off-by: Jianhui Zhao <jianhuizhao329@gmail.com>

example/helloworld.c

@@ -49,8 +49,10 @@ int main(int argc, char **argv)
 		goto err;
 	}
 
+#if (UHTTP_SSL_ENABLED)
 	if (uh_ssl_init(srv, "server-cert.pem", "server-key.pem") < 0)
 		goto err;
+#endif
 
 	uh_register_route(srv, "/test", route_test);