Null pointer dereference in EmitBooleanExpression

The following JavaScript code can lead to a null pointer de-reference.

```
function test(){
var v1 = 0;
for(var v2 = 0;;v2++){
for(var v3 = 0;;v3++){
v1 = v3;
}
}
}
test()
```

It is related to #5532 .

ChakraCore Version: ch version 1.11.15.0 (1B6EE856A9F07071BB8D11ED9068CF262DF8285FC9E762E9F77FBB6A3957E365)
Environment: 18.04.2-Ubuntu