Versions tested: 2020.2.0b11 + 10.1/Master

Steps to reproduce:

1) Have Lookdev and Game view open at the same time
2) Make sure to stay in single view layout in Lookdev, enter playmode and quit it
3) Observe that Lookdev layout resets to vertical split and throws errors.

Error stacktrace:

NullReferenceException: Object reference not set to an instance of an object
UnityEditor.Rendering.LookDev.Stage.OnBeginRendering (UnityEngine.Rendering.LookDev.IDataProvider dataProvider) (at E:/GIT/Graphics/com.unity.render-pipelines.core/Editor/LookDev/Stage.cs:247)
UnityEditor.Rendering.LookDev.Renderer.BeginRendering (UnityEditor.Rendering.LookDev.RenderingData data, UnityEngine.Rendering.LookDev.IDataProvider dataProvider) (at E:/GIT/Graphics/com.unity.render-pipelines.core/Editor/LookDev/LookDevRenderer.cs:55)