Let incomplete closure tests pass

TALES path evaluation logic was not enough to pass closure tests.
They can be passed if using this modification.
In test case, invokable object (having `__invoke` magic method) is also supported like as Closure. Not only Closure but also all callable object instances should be handled there. Conveniently, `is_callable` is already just inside `is_object` condition.

```php
if (is_object($base)) {
    if (is_callable($base)) {
    }
}
```

For consistency, I will change below code in `phptal_unravel_closure` to:

```php
while (is_object($var) && is_callable($var)) {
```