SIGSEGV in app.publish() / app.numSubscribers() on a never-subscribed topic

I'm getting segfaults when I try to publish to a topic to which no subscription has been issued. It's a pretty simple repro, basically boils down to (more descriptive repro attached). ```js import { App } from 'uWebSockets.js'; App().listen(8451, () => App().publish('never', 'hi')); // exit 139 ``` [repro-uws-segfault.js](https://github.com/user-attachments/files/27504357/repro-uws-segfault.js)