qe_rec assertion violation at ../src/qe/qsat.cpp Line: 1010

Hi,
For this formula:
```
(declare-fun a (Int) Int)
(assert (= a (lambda ((b Int)) 0)))
(check-sat-using qe_rec)
```
Z3  throws out an assertion violation:
```
ASSERTION VIOLATION
File: ../src/qe/qsat.cpp
Line: 1010
!is_lambda(e)
(C)ontinue, (A)bort, (S)top, (T)hrow exception, Invoke (G)DB
```

OS: Ubuntu 18.04
Commit: aaf2c3b
