Single weak `pagebreak` produces 0 pages

### Description

The following doc generates 0 pages:
```typst
#pagebreak(weak: true)
```

This will probably never be an issue in practice, but the specific interaction with `weak: true` may cause issues elsewhere.

### Reproduction URL

_No response_

### Operating system

Web app

### Typst version

- [X] I am using the latest version of Typst