shullker_box.png contains several transparent pixels

When copying the shulker box GUI to check its measurements (for MC-116465), I noticed that the shulker_box.png is not 176, but 203 pixel wide; upon investigating it, I found some transparent pixels to the right (203 pixels from the far left of the texture).

Currently unknown if this is also the case in 1.15.2 release and if maybe already since presumably 1.13, when all textures have been remade.

relates to MC-116465