Double invocation of commonInit()

[tjanela]

We are seeing cases of a double awakeFromNib() invocation of the WKTabBarController instance.
This causes a duplication of the container view, which in turn, might causes problems if you are relying on a particular view hierarchy for additional customisation.

There is a particular setup that might help reproducing this.
We have two segues that point to a WKTabBarController subclass on storyboards.
One storyboard contains the definition of the Scene and another storyboard uses a Storyboard Reference to execute a segue to that scene. The latter is the one that seems to trigger this double invocation.

A proposed fix is to introduce a nil check at the top of commonInit():

func commonInit() {
    if(container != nil){
        return
    }
    container = UIView()
    ...
}