Reproduction steps:(Gif in Edit)
1) Open attached project, select any sprite in the Asset window.
2) Hit Sprite Editor button in Inspector, proceed to Playmode.
3) Edit "Change Shape" "Sides" value and hit "Change" button.
4) Exit playmode and close Sprite Editor window.
5) In the pop up window select "Revert".

Error in the Edit.
Note: Whilst the error is a bad sign, further more it is misleading.
"Texture2D' has been destroyed but you are still trying to access it. Your script should either check if it is null or you should not destroy the object." which is false since there are no scripts(from users perspective).

IMPORTANT Note: Reproduction steps are valid until bug that lets you edit values mentioned above is fixed.

Workaround: Make your changes in sprite editor before going into playmode and save them.

Reproduced with: 5.3.4f1, 5.4.0b11
Can't be reproduced with any version below 5.3 since there is no way to change values mentioned above.