`:set smtFile` doesn't work with online `what4`-based provers

[RyanGlScott]

If you run this script:

:set smtFile=a.smt2
let f (x : [2]) = take y : [10] where y = x # y
:set prover=w4-z3
:sat \x -> f x == zero

With:

$ ~/Software/cryptol-2.13.0/bin/cryptol -b a.icry

Then despite having set smtFile=a.smt2, no a.smt2 file will be created. Note that a.smt2 will be created if you change prover to sbv-z3 or w4-z3, however, suggesting an inconsistency in the online what4 backend.

[RyanGlScott]

Fixed in #1476.