string->list broken in scsh-0.5.2

[nisse@lysator.liu.se (Niels Möller)]

An example session:

  [nisse@cuckoo src]$ scsh
  Scsh 0.5.2
  > (string->list "foo")
  
  Error: exception
         (string-length '())
  1>

It appears that it is the definition in scsh/lib/string-lib.scm that
is broken; the one in rts/base.scm works.

/Niels