soundness bug with  dom-simplify tactic

Hi,
I get `unsat` on this `sat` file with `(check-sat-using dom-simplify)` :

[dom-simplify.smt2](https://github.com/Z3Prover/z3/files/4472362/dom-simplify.smt2.zip)

commit: 9223f611ba6748c5e36d67c2e7d7dcc28ad4b4ff