otf to woff2 throws exception

```bash
glypher -i 'Futura-Bold.otf' -f woff2                        
wasm://wasm/00bb9f12:1


RuntimeError: unreachable
    at wasm://wasm/00bb9f12:wasm-function[1068]:0x1abb6e
    at wasm://wasm/00bb9f12:wasm-function[1458]:0x1bd81a
    at wasm://wasm/00bb9f12:wasm-function[1314]:0x1b9b0f
    at wasm://wasm/00bb9f12:wasm-function[1522]:0x1c7346