fix(webtransport): properly handle abruptly closed connections

Refreshing the page with a client connected with WebTransport would
trigger the following exception:

> node:internal/process/promises:288
>            triggerUncaughtException(err, true /* fromPromise */);
>            ^
>
> [UnhandledPromiseRejection: This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). The promise rejected with the reason "0".] {
>   code: 'ERR_UNHANDLED_REJECTION'
> }

Related: #688

lib/transports/webtransport.ts

@@ -14,7 +14,9 @@ export class WebTransport extends Transport {
     super({ _query: { EIO: "4" } });
 
     const transformStream = createPacketEncoderStream();
-    transformStream.readable.pipeTo(stream.writable);
+    transformStream.readable.pipeTo(stream.writable).catch(() => {
+      debug("the stream was closed");
+    });
     this.writer = transformStream.writable.getWriter();
 
     (async () => {