Some errors when testing on custom data with PointTransformer

### 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

I had a problem when testing a trained PointTransformer model on custom data.
RuntimeError: Tensor for 'out' is on CPU, Tensor for argument #1 'self' is on CPU, but expected them to be on GPU (while checking arguments for addmm)
or
TypeError: expected Tensor as element 0 in argument 0, but got NoneType
When the model is changed to RandLA-Net, the test works fine.
The first problem occurs when the custom data feature part is assigned a value other than None, while the second problem occurs when the custom data feature part is assigned a value of None

### Steps to reproduce the bug

```python
import open3d.ml as _ml3d
import open3d.ml.torch as ml3d # or open3d.ml.tf as ml3d
import numpy as np
import laspy

# define the model we used in the semantic segmentation task
cfg_file = r"F:\Anaconda\envs\py3_pytorch\Lib\site-packages\open3d\_ml3d\configs\pointtransformer_s3dis.yml"
cfg = _ml3d.utils.Config.load_from_file(cfg_file)
model = ml3d.models.PointTransformer(**cfg.model)

# Add path to the SemanticKitti dataset and your own custom dataset
cfg.dataset['dataset_path'] = './dataset'
cfg.dataset['custom_dataset_path'] = './pcds'

# Load the datasets
dataset = ml3d.datasets.S3DIS(cfg.dataset.pop('dataset_path', None), **cfg.dataset)
custom_dataset = load_custom_dataset(cfg.dataset.pop('custom_dataset_path', None))
print("Load dataset done!")
pipeline = ml3d.pipelines.SemanticSegmentation(model, dataset=dataset, device= "gpu", **cfg.pipeline)

# load a pre-trained model weight file
ckpt_folder = "./checkpoint/"
os.makedirs(ckpt_folder, exist_ok=True)
ckpt_path = ckpt_folder + "ckpt_00020.pth"
pipeline.load_ckpt(ckpt_path=ckpt_path)
print(pipeline.device)
print("pipeline done")

# Load test data from dataset
# test_split = dataset.get_split("test")
# data = test_split.get_data(0)

# Load test data from the custom dataset
pc_idx = 0 # change the index to get a different point cloud
print(custom_dataset[pc_idx])
data, pcd = prepare_point_cloud_for_inference(custom_dataset[pc_idx])
print("pcd done")

# Run inference
result = pipeline.run_inference(data)
print("inference done")

def load_custom_dataset(dataset_path):
print("Loading custom dataset")
pcd_paths = glob.glob(dataset_path+"/*.pcd")
pcds = []
for pcd_path in pcd_paths:
pcds.append(o3d.io.read_point_cloud(pcd_path))
return pcds

def prepare_point_cloud_for_inference(pcd):
# Remove NaNs and infinity values
pcd.remove_non_finite_points()
# Extract the xyz points
xyz = np.asarray(pcd.points)
# Set the points to the correct format for inference
data = {"point":xyz, 'feat': None, dtype=np.int32), 'label':np.zeros((len(xyz),), dtype=np.int32)}

return data, pcd
```

### Error message

RuntimeError: Tensor for 'out' is on CPU, Tensor for argument #1 'self' is on CPU, but expected them to be on GPU (while checking arguments for addmm)

TypeError: expected Tensor as element 0 in argument 0, but got NoneType

### Expected behavior

_No response_

### Open3D, Python and System information

```markdown
- Operating system: Windows 10 64-bit
- Python version: Python 3.6.12
- Open3D version: open3d-0.14
- System type: arm64
- Is this remote workstation?: yes
- How did you install Open3D?: build from source
- Compiler version (if built from source): gcc 7.5
```

### Additional information

I have not tested other models (e.g. KPConv) to see if this problem exists; perhaps it is also due to the fact that the version of Open3D I have installed is not the latest version.