Two issues with Worker demo

1) `fib.js` [default export](https://github.com/Geequlim/ECMAScriptDemos/blob/ca86889abfcd5518ed49b8f3eacf9fc4cefd91d4/worker/fib.js#L1) is `fib` function and not a godot class, so every time the file is loaded i get an error message "modules/ECMAScript/ecmascript.cpp:92 - JavaScript Error". Is this how it is supposed to be right now (work in progress)? So for now to avoid this message on every save one should export some empty class inheriting `godot.Object`?

2) This one is less straightforward. When i press "Calculate in Worker" the playing scene just exits without any error ("Calculate in Main Thread" works fine). I tested different things and it seems like there is a stack overflow in worker thread on my machine when [`N`](https://github.com/Geequlim/ECMAScriptDemos/blob/ca86889abfcd5518ed49b8f3eacf9fc4cefd91d4/worker/Control.js#L3) is higher than 26. Even when `fib` is a simple function as `(n) => n < 2 ? n : fib( n - 1 )`. With 26 or lower worker is fine. Any clues what this might be caused by? What is the maximum N on your machine if you use the provided simple function?

先在 worker 演示中复现这两份报告，然后阅读 worker/fib.js 和 worker/Control.js，尤其要查看 default export 以及 worker 计算所使用的 N 值。当重复出现的 JavaScript 错误和 worker 触发的场景退出都得到解释和修正，并且 Calculate in Main Thread 和 Calculate in Worker 路径仍按预期运行时，即视为完成。

由索引模型根据 Issue 内容生成。