Adding a plane to examples/custom_material_glsl.rs breaks cube transform

## Bevy version

0.12.1

```ignore
`AdapterInfo { name: "Apple M1", vendor: 0, device: 0, device_type: IntegratedGpu, driver: "", driver_info: "", backend: Metal }`
```

## What you did

Go to tag 0.12.1 and download examples/shaders/custom_material_glsl.rs and move to src/main.rs. Download assets/shaders/custom_material.{frag,vert} and move to the same path in the project. Edit cube's transform to (0.0, 2.0, 0.0). Run it and get
add
```
commands.spawn(PbrBundle{
mesh:meshes.add(Mesh::from(shape::Plane{size:10.0, subdivisions:0})),
transform:Transform::IDENTITY,
material:smat.add(StandardMaterial{base_color:Color::DARK_GREEN,..default()}),
..default()
});
```
To the setup function, run it and get

## What went wrong


## Additional information

I found this bug while hunting for a minimal setup of a related problem - when I add custom_material_glsl.rs to my existing project with other spawned Pbr bundles I just get

```
ERROR log: Handling wgpu errors as fatal by default
thread 'Compute Task Pool (2)' panicked at /Users/stanislavponomarev/.cargo/registry/src/index.crates.io-6f17d22bba15001f/wgpu-0.17.2/src/backend/direct.rs:3056:5:
wgpu error: Validation Error

Caused by:
In Device::create_render_pipeline
note: label = `prepass_pipeline`
Error matching ShaderStages(VERTEX) shader requirements against the pipeline
Unable to find entry point 'main'
```
Even though I didn't change the shaders and Material code, just added the spawning function to an exiting app.