[Bug]: Text tool crashes Tldraw after 3.10.1 upgrade
### What happened?

We upgraded tldraw from 3.8 to 3.10, and now attempting to create a text shape crashes the editor with the following stacktrace in Chrome:

```
TypeError: node.children is not iterable
    at visit (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:7894:30)
    at getFontsFromRichText (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:7898:3)
    at TextShapeUtil.getFontFaces (http://localhost:5173/.vite/deps/tldraw.js?v=af406af5:18641:12)
    at FontManager.shapeFontFacesCache.editor.store.createComputedCache.areResultsEqual (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:23432:26)
    at computed.isEqual [as derive] (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:10855:18)
    at __UNSAFE__Computed.__unsafe__getWithoutCapture (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:6808:27)
    at __UNSAFE__Computed.get (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:6844:19)
    at Object.get (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:10837:58)
    at FontManager.getShapeFontFaces (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:23452:37)
    at __UNSAFE__Computed.derive (http://localhost:5173/.vite/deps/chunk-NI52NUEP.js?v=f5b1ccc4:23438:69)
```

Stacktrace in Safari:

```
undefined is not an object (evaluating 'node.children')
visit@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:7894:29
getFontsFromRichText@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:7898:8
__unsafe__getWithoutCapture@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6808:33
get@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6844:46
getShapeFontFaces@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:23452:40
__unsafe__getWithoutCapture@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6808:33
get@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6844:46
@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:23442:49
__unsafe__getWithoutCapture@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6808:33
get@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6844:46
trackFontsForShape@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:23456:37
@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:29036:40
__unsafe__getWithoutCapture@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6808:33
get@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6844:46
@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:29137:63
__unsafe__getWithoutCapture@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6808:33
get@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6844:46
createTextShape@http://localhost:5173/.vite/deps/tldraw.js:11839:50
complete@http://localhost:5173/.vite/deps/tldraw.js:11812:39
onPointerUp@http://localhost:5173/.vite/deps/tldraw.js:11797:18
handleEvent@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:25839:53
handleEvent@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:25841:37
handleEvent@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:25841:37
_flushEventForTick@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:33261:26
@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:32895:34
transaction@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:6637:18
batch@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:23694:17
run@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:26783:25
_flushEventsForTick@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:32890:13
dispatch@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:32885:31
onPointerUp@http://localhost:5173/.vite/deps/chunk-NI52NUEP.js:16155:24
processDispatchQueue@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:11577:39
@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:11988:31
batchedUpdates$1@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:2539:44
dispatchEventForPluginEventSystem@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:11683:25
dispatchEvent@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:14608:46
dispatchDiscreteEvent@http://localhost:5173/.vite/deps/chunk-KB5ALOAT.js:14589:75
```

### How can we reproduce the bug?

_No response_

### What browsers are you seeing the problem on?

Chrome, Safari

### Where did this happen?

The developer package

### Contact Details

zac@constructable.ai

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct