Domine ^ is zero-width

https://fonts.google.com/specimen/Domine?preview.text=This%20is%20probably%20broken%20-%20%5E%5E%5E%5E%5E%5E%5E%5E%5E%5E%20-%20...and%20after

```shell
$ /oss/harfbuzz/build/util/hb-shape --text "^" /oss/fonts/ofl/domine/Domine\[wght].ttf
[asciicircum=0+0]
```

Suggests a collection scope check. My naive formulation was if most fonts that support a grapheme have it not-zero-width and a few have it zero that's suspect. @simoncozens suggested base glyphs shouldn't be zero width is also valid.