Closing PrefabStage throws the RegisterUndoOperation(PopFrontIfExceedsLimit) assertions into Console

Steps:

1. Add GameObject to the Hierarchy
2. Drag it to Project Browser to make a prefab
3. Open newly created prefab in isolation or inContext
4. Make changes to some of Transform value
5. Save the prefab 
6. Got to main stage (e.g. by clicking Scenes in breadcrumbs)

Result: RegisterUndoOperation(begin) - m_UndoStack.size(91) != m_UndoFilePosition.size(94) assertion thrown into Console