Bad input to the ``broadcast_to`` function triggers an internal-check error

The ``broadcast_to`` below triggers an error

```
>>> broadcast_to(model.constant([[2, 3], [4, 5]]), model.constant(5))
ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()
```

on the code checking for whether the symbol needs to be reshaped or not: ``if x.shape() == shape or (isinstance(shape, int) and x.shape() == (shape,))``