"IndexOutOfRangeException: Array index is out of range." when selecting a mix of packed and empty sprite atlases

1. Open attached project
2. Hold down CTRL (or CMD for OSX) and left-click on both atlases

"IndexOutOfRangeException: Array index is out of range." will show in the console.
Exception does not show if both atlases are packed, or if both are empty.

Tested on: 2017.1.0a6, a5

IndexOutOfRangeException: Array index is out of range.
UnityEditor.U2D.SpriteAtlasInspector.OnPreviewGUI (Rect r, UnityEngine.GUIStyle background) (at C:/Work/Trunk/Unity/Editor/Mono/2D/SpriteAtlas/SpriteAtlasInspector.cs:414)
UnityEditor.Editor.OnInteractivePreviewGUI (Rect r, UnityEngine.GUIStyle background) (at C:/Work/Trunk/Unity/artifacts/generated/common/editor/EditorBindings.gen.cs:356)
UnityEditor.ObjectPreview.DrawPreview (IPreviewable defaultPreview, Rect previewArea, UnityEngine.Object[] targets) (at C:/Work/Trunk/Unity/Editor/Mono/Inspector/Editor.cs:204)
UnityEditor.Editor.DrawPreview (Rect previewArea) (at C:/Work/Trunk/Unity/Editor/Mono/Inspector/Editor.cs:522)
UnityEditor.InspectorWindow.DrawPreviewAndLabels () (at C:/Work/Trunk/Unity/Editor/Mono/Inspector/InspectorWindow.cs:755)
UnityEditor.InspectorWindow.OnGUI () (at C:/Work/Trunk/Unity/Editor/Mono/Inspector/InspectorWindow.cs:395)
System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Reflection/MonoMethod.cs:222)