qsat assertion violation at ../src/qe/qsat.cpp Line: 633

Hi,
For this formula:
```
(declare-fun a () (Array Int (Array Int Int)))
(assert (= a (store a 0 (store (select a 0) 0 0))))
(check-sat-using qsat)
```
Z3  throws out an assertion violation:
```
ASSERTION VIOLATION
File: ../src/qe/qsat.cpp
Line: 633
validate_defs("check_sat")
(C)ontinue, (A)bort, (S)top, (T)hrow exception, Invoke (G)DB
```

OS: Ubuntu 18.04
Commit: 99b71a9
