Bytes per pixel should be multiplied by width before calling align_copy_bytes_per_row

[allenqm]

I was playing around with the headless_renderer.rs example. I observed that image_data received in the update system was 4x the size I was expecting. I set the dimensions to 64x64 in AppConfig; image_data.len was 65k bytes vs the expected 16k.

I think it's due how the cpu buffer is initialized in ImageCopier::new()

pub fn new(
        src_image: Handle<Image>,
        size: Extent3d,
        render_device: &RenderDevice,
    ) -> ImageCopier {
        let padded_bytes_per_row =
            RenderDevice::align_copy_bytes_per_row((size.width) as usize) * 4;  // HERE: shouldn't we multiply by 4 before calling align_copy_bytes_per_row?

        let cpu_buffer = render_device.create_buffer(&BufferDescriptor {
            label: None,
            size: padded_bytes_per_row as u64 * size.height as u64,
            usage: BufferUsages::MAP_READ | BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        ImageCopier {
            buffer: cpu_buffer,
            src_image,
            enabled: Arc::new(AtomicBool::new(true)),
        }
    }

When I make the suggested change, I get the expected image_data length.

I'm relatively new to rendering code, so wanted to confirm this is an error first. If it is, I can submit a simple PR to fix.