ArgumentException is thrown on opening HDRP Compositor window after deleting Composite assets from the Project window.

Steps to repro:
1. Create a new HDRP template project
2. Windows > Render Pipeline > HD Render Pipeline Compositor.
3. Enable Compositor > Close the Compositor window.
4. Delete Compositor folder in Project Window.
5. Windows > Render Pipeline > HD Render Pipeline Compositor.

Actual Result:
ArgumentException errors are thrown in the console.

Expected Result:
No error in the console.

Reproducible in:
2020.2.0a18, 2020.1.0b16, 2020.1.0b13 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:
ArgumentException: Invalid path
System.IO.Path.GetDirectoryName (System.String path) (at <fb001e01371b4adca20013e0ac763896>:0)
UnityEditor.Rendering.HighDefinition.Compositor.CompositionUtils.LoadOrCreateCompositionProfileAsset (UnityEngine.Rendering.HighDefinition.Compositor.CompositionManager compositor) (at library/packagecache/com.unity.render-pipelines.high-definition@9.0.0-preview.33/editor/compositor/compositionutils.cs:95)
UnityEditor.Rendering.HighDefinition.Compositor.CompositorWindow.OnGUI () (at library/packagecache/com.unity.render-pipelines.high-definition@9.0.0-preview.33/editor/compositor/compositorwindow.cs:112)
UnityEditor.HostView.InvokeOnGUI (UnityEngine.Rect onGUIPosition, UnityEngine.Rect viewRect) (at <833199c02ee84e91a3a7100aef51217f>:0)
UnityEditor.DockArea.DrawView (UnityEngine.Rect viewRect, UnityEngine.Rect dockAreaRect) (at <833199c02ee84e91a3a7100aef51217f>:0)
UnityEditor.DockArea.OldOnGUI () (at <833199c02ee84e91a3a7100aef51217f>: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 <434515d9f4bb4f26bab9aa61f75e4922>:0)
UnityEngine.GUIUtility:ProcessEvent(Int32, IntPtr, Boolean&)