UICollectionView layout not invalidated on device rotation

[esilverberg]

The UICollectionView .collectionViewLayout is not being properly invalidated on a rotation. This leads to the following, easily-reproable behavior (do this on the "Empty Chat" screen of the demo app):

The solution is fairly straightforward -- just call

collectionView.collectionViewLayout.invalidateLayout()

in the method viewWillTransition of BaseChatViewController.