open3d.ml.torch.layers.KNNSearch failed when more than 20 million points

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D-ML/issues).
- [X] I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### Describe the issue

Hi, all. I found out that open3d.ml.torch.layers.KNNSearch failed to generate the results when there are about more than 20 million points. The program just exits at `ans = nsearch(points, queries, K)` without warning message.

Is there any workaround or anything else I have missed here? Thanks in advance!!!

### Steps to reproduce the bug

```python
import open3d.ml.torch as ml3d
import torch

points = torch.from_numpy(xyz)
queries = torch.from_numpy(xyz)

nsearch = ml3d.layers.KNNSearch(return_distances=True)
ans = nsearch(points, queries, K)

neighbors_index = ans.neighbors_index.reshape(xyz.shape[0],K)
neighbors_distance = ans.neighbors_distance.reshape(xyz.shape[0],K)
```
```

### Error message

_No response_

### Expected behavior

_No response_

### Open3D, Python and System information

```markdown
- Operating system: (e.g. OSX 10.15, Ubuntu 18.04, Windows 10 64-bit)
- Python version: (e.g. Python 3.8 / output from `import sys print(sys.version)`)
- Open3D version: (output from python: `print(open3d.__version__)`)
- System type: (x84 / arm64 / apple-silicon / jetson / rpi)
- Is this remote workstation?: yes or no
- How did you install Open3D?: (e.g. pip, conda, build from source)
- Compiler version (if built from source): (e.g. gcc 7.5, clang 7.0)
```

### Additional information

_No response_