hasAttachments function should test if attachments property exists

I propose to change

```
commentModel.hasAttachments = function() {
    return commentModel.attachments.length > 0;
}
```

to

```
commentModel.hasAttachments = function() {
    return !!commentModel.attachments && commentModel.attachments.length > 0;
}
```

as `commentModel` does not always contain `attachments` property 👍