KSampler (Advanced)'s add_noise parameter is not handled correctly when it is disabled

### Custom Node Testing

- [x] I have tried disabling custom nodes and the issue persists (see [how to disable custom nodes](https://docs.comfy.org/troubleshooting/custom-node-issues#step-1%3A-test-with-all-custom-nodes-disabled) if you need help)

### Expected Behavior

When add_noise in KSampler (Advanced) node is disabled, there's no noise added and latent_image is used as is.

### Actual Behavior

When add_noise in KSampler (Advanced) node is disabled, a new empty image is created which is quite different from the expected behavior.
https://github.com/comfyanonymous/ComfyUI/blob/bbb11e26081977474eec72ce36d12ec778b5a9ea/nodes.py#L1493-L1494

### Steps to Reproduce

N/A

### Debug Logs

```powershell
N/A
```

### Other

This bug prevents from using the noise generated outside of KSampler and using it as a latent_image input.