(ufbv) Assertion violation at ../src/ast/rewriter/rewriter_def.h Line: 83

Hi,
For this formula:
```
(declare-fun a (Int Bool) Bool)
(assert (= a (lambda ((b Int) (c Bool)) c)))
(check-sat-using ufbv)
```
Z3  throws out an assertion violation:
```
ASSERTION VIOLATION
File: ../src/ast/rewriter/rewriter_def.h
Line: 83
st != BR_DONE || m().get_sort(m_r) == m().get_sort(t)
(C)ontinue, (A)bort, (S)top, (T)hrow exception, Invoke (G)DB
```

OS: Ubuntu 18.04
Commit: 179c9c2
