Herbie20 crashes on FPCore but Herbie10 behaves normally

[JonasRegehr]

The Herbie20 platform crashes on this FPCore:

(FPCore (x)
  (if (> (fabs (cos x)) 0.0)
      (/ 1.0 (cos x))
      0.0))

With this error:

  inexact?: contract violation
    expected: number?
    given: #t

But the Herbie10 platform works fine.

Run
racket src/main.rkt report --platform herbie20 --seed 42 crashes.fpcore out-herbie20 and
racket src/main.rkt report --platform herbie10 --seed 42 crashes.fpcore out-herbie10
on the herbie20-crash branch to recreate.