Fixed autolayout error

An AutoLayout error occurred every time the video player was launched.

`Unable to simultaneously satisfy constraints.`

I believe it was due to one of the UI elements not having enough space. I believe the problem is in `GMFPlayerOverlayViewController.m`, where the `loadView` function creates a `CGRect` called `frameRect`. When `frameRect` is created, `_playerOverlayView` is `nil`, so `frameRect` ends up with a height of `0` and a width of `0`.

To fix this, I've made it so that `frameRect` takes up the full size of the screen.

The error no longer appears and there don't seem to be any changes in performance/functionality.
Won't this cause problems when we want to load the player in a non-fullscreen context? Seems like this will need to change soon anyway.