fix(node/http): don't throw on .address() before .listen() (#24432)

It's perfectly valid to access `server.address()` before calling
`.listen()`. Until a server actively listens on a socket Node will
return `null` here, but we threw a "Cannot access property 'port' of
undefined" instead.

This was discovered when inspecting failures in Koa's test suite with
Deno.

ext/node/polyfills/http.ts

@@ -1657,7 +1657,7 @@ export class ServerImpl extends EventEmitter {
   #httpConnections: Set<Deno.HttpConn> = new Set();
   #listener?: Deno.Listener;
 
-  #addr: Deno.NetAddr;
+  #addr: Deno.NetAddr | null = null;
   #hasClosed = false;
   #server: Deno.HttpServer;
   #unref = false;
@@ -1843,6 +1843,7 @@ export class ServerImpl extends EventEmitter {
   }
 
   address() {
+    if (this.#addr === null) return null;
     return {
       port: this.#addr.port,
       address: this.#addr.hostname,

tests/unit_node/http_test.ts

@@ -1251,3 +1251,8 @@ Deno.test("[node/http] http.request() post streaming body works", async () => {
   clearTimeout(timeout);
   assertEquals(server.listening, false);
 });
+
+Deno.test("[node/http] Server.address() can be null", () => {
+  const server = http.createServer((_req, res) => res.end("it works"));
+  assertEquals(server.address(), null);
+});