Cast does not work on array access properly

This works,
```
public var BinaryNode<E> left <=> (BinaryNode<E>)(this[0])
```
but this...
```
public var BinaryNode<E> left <=> (BinaryNode<E>)this[0]
```
... is parsed like `(BinaryNode<E>)this` instead of `(BinaryNode<E>)this[0]`