Bug in nested lambda

• Test code

(define (bar x)
  (foo))

(define (foo)
  (lambda (y)    
    120))

((bar 10) 20)

• Error message

Backtrace:
In ice-9/boot-9.scm:
  1736:10 10 (with-exception-handler _ _ #:unwind? _ # _)
In unknown file:
           9 (apply-smob/0 #<thunk 7fa1cc020d60>)
In ice-9/boot-9.scm:
    718:2  8 (call-with-prompt _ _ #<procedure default-prompt-handle…>)
In ice-9/eval.scm:
    619:8  7 (_ #(#(#<directory (guile-user) 7fa1cc01ac80>)))
In laco/compile.scm:
   255:25  6 (laco-compile _)
   202:36  5 (run-till-stage _ opt)
    145:4  4 (optimize #<r6rs:record:letcont/k>)
In unknown file:
           3 (hash-for-each #<procedure 7fa1cbad78e0 at laco/compil…> …)
In laco/compile.scm:
   149:27  2 (_ #{#lifted-247}# _)
In srfi/srfi-1.scm:
   460:18  1 (fold #<procedure 7fa1cbad7ef8 at laco/compile.scm:113…> …)
In laco/compile.scm:
    113:4  0 (_ _ _)

laco/compile.scm:113:4: BUG: invalid type #<r6rs:record:gvar>