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I experienced the same issue. Dirty hotfix in case you don't want to wait for the official fix ^^: create a folder "images" inside the "game" folder with three files: magic_3.png, vervain.png and wax.png. I just created white 50x50px images and wrote "Vervain", "Wax" and "Dust" on it but you can really use any picture I guess.
That should work without error. You just have three potentially ugly, though small, pictures inside the wardrobe with the potions, but you can progress without any issues. At least that worked for me.

As long as you dont click on the potion in the wardrobe it should be fine. I could progress by just talking to the sisters after brewing the potion