url: handle unicode hostname if empty

PR-URL: #49396
Fixes: #48759
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

Author: anonrig

src/node_url.cc

@@ -208,7 +208,7 @@ void BindingData::Format(const FunctionCallbackInfo<Value>& args) {
     out->hash = std::nullopt;
   }
 
-  if (unicode) {
+  if (unicode && out->has_hostname()) {
     out->host = ada::idna::to_unicode(out->get_hostname());
   }
 

test/parallel/test-url-format-whatwg.js

@@ -140,3 +140,8 @@ assert.strictEqual(
   url.format(new URL('http://user:pass@xn--0zwm56d.com:8080/path'), { unicode: true }),
   'http://user:pass@测试.com:8080/path'
 );
+
+assert.strictEqual(
+  url.format(new URL('tel:123')),
+  url.format(new URL('tel:123'), { unicode: true })
+);