Bug: function default parameter wrapped in extraneous parenthesis when part of boolean expression

### Input Code

```coffee
false or (a, b = {}) -> null
```

### Expected Behavior
```coffee
false || function(a, b = {}) {
  return null;
};
```

### Current Behavior
```coffee
false || function(a, (b = {})) {
  return null;
};
```

### Environment

* CoffeeScript version: 2.3.2
* Node.js version: 10.12.0
