Regression on simple NIA formula

d5c6abe
```
$z3-4.8.8 bug.smt2
unsat
$z3-4.8.9 bug.smt2
unsat
$z3-4.8.10 bug.smt2
unsat
$z3release bug.smt2 
unknown
$time z3release smt.mbqi.max_iterations=1000000 bug.smt2
unknown
z3release smt.mbqi.max_iterations=1000000 bug.smt2  146.67s user 0.01s system 99% cpu 2:26.72 total
$
$cat bug.smt2 
(declare-const x Int)
(assert (forall ((v Int)) (= v (* x x))))
(check-sat)

```