ostrich returns `sat` for an `unsat` formula with `re.none`

[wingsyuyi-satori]

I found a soundness bug in ostrich when solving a very simple formula. The formula is as follows:

(set-logic QF_S)
(assert (= re.none (str.to_re "glggfufacvzlgldjlvpwisbszm")))
(check-sat)

z3 correctly returns unsat for this input, while ostrich returns sat.

https://eldarica.org/ostrich/?ex=perma%2F1775133145_1707703174

[wingsyuyi-satori]

Looks like it's for the same reason as this issue?
#96