When a block texture is unavailable, other random block textures are displayed

The bug

Parent bug of MC-145275 and MC-153547. When a texture is called but it doesn't exist, whether it be because the texture is too small or that it doesn't exist at all, random other block textures from the texturemap are called instead leaving a mash of jumbled textures. The missing texture block only covers up this glitch (see MC-153547 for more info).

Example

Model file barrel.json (which calls file barrel.png) uses the maximum size a block can be, 48x48, resulting in: 2019-07-06_08.03.01.png

How to reproduce: Add the barrel.json file to a resource pack in the models/blocks folder.