refreshCompletion getting called on addPullToRefresh / viewDidLoad

The refreshCompletion block is getting called while the view is loading.

After debugging I've found that this condition is being executed while the view is loading / appearing:

```
public override func observeValueForKeyPath(...) {
(...)
if (scrollView.dragging == false && self.state != .Refreshing) {
self.state = .Refreshing
}
(...)
```