bug#13188: par-map causes VM stack overflow

[Nala Ginrut]

Here is the error message.
Anyway, par-map shouldn't cause stack overflow.

-----------------------err msg------------------------------
scheme@(guile-user)> (par-map 1+ (iota 10000))
While executing meta-command:
ERROR: Throw to key `vm-error' with args `(vm-run "VM: Stack
overflow" ())'.
-------------------------end--------------------------------