@internal tag crashes documentationjs if indexed type follows

```typescript
/** @internal */
export type AnyObj = { [key: string]: any };
```

this will crash documentation

```
$ npx documentation readme src/** --readme-file=API.md --section=API --parse-extension ts --shallow --resolve node --config documentation.yaml
TypeError: Cannot read property 'charAt' of undefined
at Of.inlineCode (/.../node_modules/remark-stringify/lib/visitors/inline-code.js:26:13)
```

This is an officially supported typescript tag.

Interestingly it only seems to happen when using an indexed object type like the above with the internal tag specifically