(ctx-solver-simplify) Assertion violation at ../src/math/lp/nla_core.cpp Line: 1500

Hi,
For this formula:
```
(assert (forall ((a Int) (b Int)) (distinct (div a b) 0)))
(check-sat-using ctx-solver-simplify)
```
Z3  throws out an assertion violation:
```
ASSERTION VIOLATION
File: ../src/math/lp/nla_core.cpp
Line: 1500
elists_are_consistent(true)
(C)ontinue, (A)bort, (S)top, (T)hrow exception, Invoke (G)DB
```

OS: Ubuntu 18.04
Commit: a14c2a3
