Sometimes incorrect layout guides when pushing a view controller into a stack controller

[defagos]

Sometimes the top layout guide might not be correctly propagated to the child view controller.

After spending too much time investigating this issue (without real success), I stumbled upon the probable cause: before iOS 11, -addChildViewController: must be called after the child view controller view has been added to its parent container, so that layout guides are correctly propagated.

The issues seems to disappear with iOS 11 and the new safe area concept. It is probably not so relevant anymore to address it.