Refutation soundness issue on a string formula

Commit: https://github.com/cvc5/cvc5/commit/5e6117cc183513bf676b36078e6507b31caa6ff0
OS: Ubuntu 18.04

```
[596] % cvc5 -q small.smt2
unsat
[597] % cvc4-1.8 -q small.smt2
unsat
[598] % z3 small.smt2
sat
[599] % cat small.smt2
(assert (str.in_re "A" (ite (= (div 0 0) 0) (str.to_re "A") (str.to_re "B"))))
(check-sat)
[600] % 
```