[2D] Newly created Sprite Mask has Sprite preset to a latest sliced Sprite

Steps to Repro:

1. import a Texture
2. set the Texture Type to Sprite (2D and UI) and the Sprite Mode to Multiple
3. click on Sprite Editor to access the Sprite Editor window
4. Slice the image, Apply it, and close the window
5. go to the Hierarchy and create a New Sprite Mask

Result: The New Sprite Mask will have its Sprite preset to the recently sliced sprite
Expected: The Sprite setting should be set to None.