Output fails ots-sanitize, can’t be loaded in Firefox nightly
After processing a TrueType font with `fontmin --text`, the output can’t be loaded as a web font in Firefox nightly. This is because the output fails the validation enabled by the **gfx.downloadable_fonts.otl_validation** preference, which is true by default in Firefox nightly. This can also be reproduced using the standalone [OpenType Sanitizer](https://github.com/khaledhosny/ots) project on which Firefox’s validation is based.

### Reproduction steps

Install OpenType Sanitizer.

```console
$ git clone https://github.com/khaledhosny/ots.git
$ cd ots
$ meson build
$ ninja -C build
$ ninja -C build install
$ cd ..
```

Downgrade `get-stdin` and `meow` in `fontmin` to work around #97.

```console
$ git clone https://github.com/ecomfe/fontmin.git
$ cd fontmin
$ npm i get-stdin@^8 meow@^9
```

Get a font, and demonstrate that it passes sanitization.

```console
$ curl -LO 'https://github.com/adobe-fonts/source-sans/raw/3.046R/TTF/SourceSans3-Bold.ttf'
$ ots-sanitize SourceSans3-Bold.ttf sanitized.ttf
File sanitized successfully!
```

Process the font with `fontmin`, and demonstrate that the result fails sanitization.

```console
$ ./cli.js --text abc SourceSans3-Bold.ttf > out.ttf
$ ots-sanitize out.ttf sanitized.ttf
ERROR at ../src/layout.cc:380 (ParseCoverageFormat2)
ERROR: Layout: bad range count: 8
ERROR at ../src/gpos.cc:631 (ParseMarkToAttachmentSubtables)
ERROR: GPOS: Failed to parse converge 1 table
ERROR at ../src/layout.cc:1178 (Parse)
ERROR: Layout: Failed to parse lookup subtable 3
ERROR at ../src/layout.cc:240 (ParseLookupTable)
ERROR: Layout: Failed to parse subtable 0
ERROR at ../src/layout.cc:1328 (ParseLookupListTable)
ERROR: Layout: Failed to parse lookup 0
ERROR: GPOS: Failed to parse lookup list table
ERROR at ../src/ots.cc:711 (ProcessGeneric)
ERROR: GPOS: Failed to parse table
Failed to sanitize file!
```

Alternatively, write an HTML file that uses the output font and view it in Firefox nightly. The output font is not displayed, and a corresponding set of errors shows up in the browser console.

```html
<!-- test.html -->
<meta charset="UTF-8" />
<style>
  @font-face {
    font-family: InputFont;
    src: url(SourceSans3-Bold.ttf);
  }
  @font-face {
    font-family: OutputFont;
    src: url(out.ttf);
  }
</style>
<div style="font-family: InputFont">abc</div>
<div style="font-family: OutputFont">abc</div>
```

![Screenshot from 2021-10-25 19-19-43](https://user-images.githubusercontent.com/26471/138797665-32d7efff-e198-4178-a947-f84050a6f606.png)
