bv assertion violation at ../src/ast/macros/macro_manager.cpp Line: 280

Hi,
For this formula:
```
(declare-sort E 0)
(declare-fun f (E) Bool)
(declare-fun g (E) E)
(assert (forall ((a E)) (f (g a))))
(check-sat-using bv)
```
Z3  throws out an assertion violation:
```
ASSERTION VIOLATION
File: ../src/ast/macros/macro_manager.cpp
Line: 280
v->get_idx() < num
(C)ontinue, (A)bort, (S)top, (T)hrow exception, Invoke (G)DB
```

OS: Ubuntu 18.04
Commit: d25db0d
