Packaging syn crashes on an unwrap feature dependency syn-test-suite

The failing unwrap() call happens in src/crates.rs - and right above it there is a comment indicating that the unwrap is ok because it would only fail with invalid Cargo.tom files:

unwrap is ok, valid Cargo.toml files must have this

I can't tell whether the Cargo.toml for syn is in fact invalid, or whether the expectation of the code in crates.rs is wrong.

When simply ignoring the not-found entries of the deps_by_name variable, e.g. by placing it inside an if let Some(…) = block, the packaging works properly for this crate.