fix(uws): prevent the server from crashing after upgrade

This should fix a rare case where the Engine.IO connection was upgraded
to WebSocket while the Socket.IO socket was disconnected, which would
result in the following exception:

> TypeError: Cannot read properties of undefined (reading 'forEach')
>    at subscribe (/node_modules/socket.io/dist/uws.js:87:11)
>    at Socket.<anonymous> (/node_modules/socket.io/dist/uws.js:28:17)
>    at Socket.emit (node:events:402:35)
>    at WebSocket.onPacket (/node_modules/engine.io/build/socket.js:214:22)
>    at WebSocket.emit (node:events:390:28)
>    at WebSocket.onPacket (/node_modules/engine.io/build/transport.js:92:14)
>    at WebSocket.onData (/node_modules/engine.io/build/transport.js:101:14)
>    at message (/node_modules/engine.io/build/userver.js:56:30)

Related: #4443

lib/uws.ts

@@ -25,7 +25,9 @@ export function patchAdapter(app /* : TemplatedApp */) {
     if (isNew) {
       socket.conn.on("upgrade", () => {
         const rooms = this.sids.get(id);
-        subscribe(this.nsp.name, socket, isNew, rooms);
+        if (rooms) {
+          subscribe(this.nsp.name, socket, isNew, rooms);
+        }
       });
     }
   };

test/uws.ts

@@ -186,6 +186,12 @@ describe("socket.io with uWebSocket.js-based engine", () => {
     io.to("room1").emit("hello");
   });
 
+  it("should not crash when socket is disconnected before the upgrade", (done) => {
+    client.on("disconnect", () => done());
+
+    io.of("/").sockets.get(client.id)!.disconnect();
+  });
+
   it("should serve static files", (done) => {
     const clientVersion = require("socket.io-client/package.json").version;