Sliced definition of let-syntax inside of let raises an error

[Takashi Kato]

This should return b but raises an error

(import (rnrs))

(let ()
  (let-syntax ()
    (define foo 'b))
  foo)

Originally from this tweet: https://twitter.com/SaitoAtsushi/status/1063342409994498048

[Takashi Kato]

If the let-syntax contains bindings it doesn't happen

[Takashi Kato]

Fixed in <<79a706e>>