Sign textures don't display correctly if the resource pack isn't 16x16

Can be reproduced with e.g. [Faithful 32x](https://faithfulpack.net/faithful32x). However they _do_ seem to work with 8x8 resource packs.

<img width="826" height="478" alt="Image" src="https://github.com/user-attachments/assets/d04afbe3-6af0-4019-872f-9cb8444bb589" />

Possibly related to #1259 