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, a random other block texture is 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