fix(uws): handle invalid websocket upgrades

When binding to an uWebSockets.js App, there was an unhandled case that
could crash the server:

```
curl "http://localhost:3000/engine.io/?EIO=4&transport=websocket"
```

would result in:

```
Error: Returning from a request handler without responding or attaching an abort handler is forbidden!
terminate called without an active exception
```

Note: this does not apply to the default server based on ws, because
the error was caught elsewhere in the source code.

Related: socketio/socket.io#4250

lib/server.ts

@@ -245,6 +245,13 @@ export abstract class BaseServer extends EventEmitter {
         });
       }
 
+      if (transport === "websocket" && !upgrade) {
+        debug("invalid transport upgrade");
+        return fn(Server.errors.BAD_REQUEST, {
+          name: "TRANSPORT_HANDSHAKE_ERROR"
+        });
+      }
+
       if (!this.opts.allowRequest) return fn();
 
       return this.opts.allowRequest(req, (message, success) => {

lib/userver.ts

@@ -28,6 +28,10 @@ export class uServer extends BaseServer {
     req.connection = {
       remoteAddress: Buffer.from(res.getRemoteAddressAsText()).toString()
     };
+
+    res.onAborted(() => {
+      debug("response has been aborted");
+    });
   }
 
   protected createTransport(transportName, req) {

test/server.js

@@ -603,9 +603,6 @@ describe("server", () => {
     });
 
     it("should disallow bad requests (handshake error)", function(done) {
-      if (process.env.EIO_WS_ENGINE === "uws") {
-        return this.skip();
-      }
       const partialDone = createPartialDone(done, 2);
 
       engine = listen(
@@ -618,8 +615,6 @@ describe("server", () => {
             expect(err.code).to.be(3);
             expect(err.message).to.be("Bad request");
             expect(err.context.name).to.be("TRANSPORT_HANDSHAKE_ERROR");
-            expect(err.context.error).to.be.an(Error);
-            expect(err.context.error.name).to.be("TypeError");
             partialDone();
           });