[Flight] Treat empty message as a close signal (facebook#33756)

We typically treat an empty message as closing the debug channel stream
but for the Noop renderer we don't use an intermediate stream but just
pass the message through.


https://github.com/facebook/react/blob/bbc13fa17be8eebef3e6ee47f48c76c0c44e2f36/packages/react-server-dom-webpack/src/client/ReactFlightDOMClientBrowser.js#L59-L60

For that simple case we should just treat it as a close without an
intermediate stream.

Author: sebmarkbage

packages/react-server/src/ReactFlightServer.js

@@ -5808,6 +5808,10 @@ export function resolveDebugMessage(request: Request, message: string): void {
       "resolveDebugMessage/closeDebugChannel should not be called for a Request that wasn't kept alive. This is a bug in React.",
     );
   }
+  if (message === '') {
+    closeDebugChannel(request);
+    return;
+  }
   // This function lets the client ask for more data lazily through the debug channel.
   const command = message.charCodeAt(0);
   const ids = message.slice(2).split(',').map(fromHex);