Improve terrain texture asset handling

crates/terrain/src/plugin.rs

@@ -64,7 +64,8 @@ fn setup_textures(
  LoadState::Failed => panic!("Texture loading has failed."),
  LoadState::Loaded => {
  // Ideally, this setup would happen in some kind of asset post
- // processing. This is however not yet supported by Bevy.
+ // processing. This was not supported by Bevy at the time of
+ // implementation.
  //
  // https://github.com/bevyengine/bevy/discussions/3972
  let image = images.get_mut(&textures.0).unwrap();
@@ -77,8 +78,7 @@ fn setup_textures(
  true.into()
  }
  },
- // TODO: Is this correct?
- None => false.into(),
+ None => panic!("Terrain texture asset unknown."),
  }
 }