Bug 259439

I noticed awaiting a promise after an error was thrown in a JavaScript module does not actually throw the error.
window.onerror is never called, and the JavaScript console is empty.

```
<script type="module">
  throw new Error();
  // Adding this line will never throw the error in JavaScript console.
  await Promise.resolve();
</script>
```

Note that I can't reproduce in Chrome and Firefox.

Demo: https://early-glamorous-botany.glitch.me/