-ArgumentOutOfRangeException errors on undoing after removing all sublayers in Render Schedule in Graphics Compositor.
-Graphics Compositor window broke and GUI errors are thrown in the console.

Steps to repro:
1. Create a new HDRP template project
2. Windows > Render Pipeline > Graphics Compositor.
3. Enable Compositor > Render Schedule > Add Image.
4. Add Video > Change the sequence of the sublayers.
5. Remove all Sublayers > Press CTRL + Z.

Actual Result:
ArgumentOutOfRangeException & GUI errors are thrown in the console.

Expected Result:
No errors in the console.

Reproducible in:
2020.2.0a20 with Package version 10.0.0-preview.27.

Working Fine in:
2020.2.0a20 with Package version 9.0.0-preview.33.

Note: HDRP Compositor window introduced in 9.0.0 preview.33.

Environment:
Occurring on Windows 10 & Mac 10.15.

Stacktrace:
ArgumentOutOfRangeException: Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index
System.ThrowHelper.ThrowArgumentOutOfRangeException (System.ExceptionArgument argument, System.ExceptionResource resource) (at <fb001e01371b4adca20013e0ac763896>:0)
System.ThrowHelper.ThrowArgumentOutOfRangeException () (at <fb001e01371b4adca20013e0ac763896>:0)
System.Collections.Generic.List`1[T].get_Item (System.Int32 index) (at <fb001e01371b4adca20013e0ac763896>:0)
UnityEditor.Rendering.HighDefinition.Compositor.CompositionManagerEditor.OnInspectorGUI () (at library/packagecache/com.unity.render-pipelines.high-definition@10.0.0-preview.27/editor/compositor/compositionmanagereditor.cs:265)
UnityEditor.Rendering.HighDefinition.Compositor.CompositorWindow.OnGUI () (at library/packagecache/com.unity.render-pipelines.high-definition@10.0.0-preview.27/editor/compositor/compositorwindow.cs:139)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at <70c42c992fa442f8aa9edcf3e9f7b431>:0)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect) (at <70c42c992fa442f8aa9edcf3e9f7b431>:0)
UnityEditor.DockArea.OldOnGUI () (at <70c42c992fa442f8aa9edcf3e9f7b431>:0)
UnityEngine.UIElements.IMGUIContainer.DoOnGUI (UnityEngine.Event evt, UnityEngine.Matrix4x4 parentTransform, UnityEngine.Rect clippingRect, System.Boolean isComputingLayout, UnityEngine.Rect layoutSize, System.Action onGUIHandler, System.Boolean canAffectFocus) (at <d683819026f84051943436699bfd6120>:0)
UnityEditor.EditorApplication:Internal_CallGlobalEventHandler()

GUI Error: You are pushing more GUIClips than you are popping. Make sure they are balanced.
UnityEditor.EditorApplication:Internal_CallGlobalEventHandler ()