Syntax: Recover on bad enum syntax.

[ehuss]

Break out of highlighting an enum definition when there is invalid syntax. This often happens with things like serde's forward_to_deserialize_any, it would get confused for many lines following.

    serde::forward_to_deserialize_any! {
        f32 f64 char str bytes
        byte_buf unit unit_struct
        enum identifier ignored_any newtype_struct
    }