qe segmentation fault on BV formula

Hi,
For this formula,
```
(assert (forall ((a (_ BitVec 6))) (forall ((b (_ BitVec 6))) (forall ((c (_ BitVec 6))) (or (distinct a b c) (= b c))))))
(check-sat-using qe)
```
z3 throws out a segmentation fault.

OS: Ubuntu 18.04
Commit: aaf2c3b