Remove - while setting collapsed constraints for MessageViewController

Sorry for not openning PR, I made a lot of changes, so dont want to push it here :)

```
private func makeCollapsedConstraints() -> [NSLayoutConstraint] {
return [
messageView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
messageView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
messageView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
messageView.heightAnchor.constraint(
equalToConstant: hideFooterView ? 0 : -BarcodeScannerViewController.footerHeight
)
]
}
```

Here I think `-BarcodeScannerViewController.footerHeight` should be `BarcodeScannerViewController.footerHeight` height can not be negative.