wit-bindgen grain does not support inline interfaces

[godotdot]

Inline interfaces do not work.

For instance, trying to use wit-bindgen on the attached inline.wit:

wit-bindgen grain inline.wit 
thread 'main' panicked at crates/grain/src/lib.rs:145:18:
called `Option::unwrap()` on a `None` value
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace`

However, it is possible to work around this by not using inline interfaces:

wit-bindgen grain workaround.wit 
Generating "convert.gr"

wit_files.zip

Version information:

git log -n 1
commit d152684804a35761de51bc541f7379bcdf330b9c (HEAD -> grain, origin/grain)
Author: Oscar Spencer <oscar@grain-lang.org>
Date:   Thu May 9 08:38:45 2024 -0500

    fix s32 bindgen

wit-bindgen --version            
wit-bindgen-cli 0.21.0 (a37b0c143 2024-04-05)