Repository: pytorch
Issue: `unfold` fails in forward mode when unfolding a scalar tensor
Labels: triaged,module: forward ad

### 🐛 Describe the bug

`unfold` fails in forward mode when unfolding a scalar tensor but succeeds in reverse mode.

```py
import torch
from torch.autograd.functional import jacobian

inp = torch.rand([], dtype=torch.float64)

def func(inp):
    res = inp.unfold(0,1,1)
    return res

print(func(inp))
# tensor([0.4578], dtype=torch.float64)
print(jacobian(func, (inp,), vectorize=True, strategy="reverse-mode"))
# (tensor([1.], dtype=torch.float64),)
print(jacobian(func, (inp,), vectorize=True, strategy="forward-mode"))
# Fail
# IndexError: Dimension out of range (expected to be in range of [-1, 0], but got 1)
```

Actually, I am not sure whether the direct call should raise an error since the 0-dim would be *undefined* for scalar tensor. But at least the behavior should be consistent for all cases.

### Versions

```
PyTorch version: 2.0.0.dev20230105
Is debug build: False
CUDA used to build PyTorch: 11.7
ROCM used to build PyTorch: N/A

OS: Ubuntu 22.04.1 LTS (x86_64)
GCC version: (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
Clang version: Could not collect
CMake version: version 3.22.1
Libc version: glibc-2.35

Python version: 3.9.15 (main, Nov 24 2022, 14:31:59)  [GCC 11.2.0] (64-bit runtime)
Python platform: Linux-5.15.0-56-generic-x86_64-with-glibc2.35
Is CUDA available: True
CUDA runtime version: 11.7.99
CUDA_MODULE_LOADING set to: LAZY
GPU models and configuration:
GPU 0: NVIDIA GeForce RTX 3090
GPU 1: NVIDIA GeForce RTX 3090
GPU 2: NVIDIA GeForce RTX 3090

Nvidia driver version: 515.86.01
cuDNN version: Probably one of the following:
/usr/lib/x86_64-linux-gnu/libcudnn.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_adv_infer.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_adv_train.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_cnn_infer.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_cnn_train.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_ops_infer.so.8.4.1
/usr/lib/x86_64-linux-gnu/libcudnn_ops_train.so.8.4.1
HIP runtime version: N/A
MIOpen runtime version: N/A
Is XNNPACK available: True

Versions of relevant libraries:
[pip3] numpy==1.23.5
[pip3] torch==2.0.0.dev20230105
[pip3] torchaudio==2.0.0.dev20230105
[pip3] torchvision==0.15.0.dev20230105
[conda] blas                      1.0                         mkl
[conda] mkl                       2021.4.0           h06a4308_640
[conda] mkl-service               2.4.0            py39h7f8727e_0
[conda] mkl_fft                   1.3.1            py39hd3c417c_0
[conda] mkl_random                1.2.2            py39h51133e4_0
[conda] numpy                     1.23.5           py39h14f4228_0
[conda] numpy-base                1.23.5           py39h31eccc5_0
[conda] pytorch                   2.0.0.dev20230105 py3.9_cuda11.7_cudnn8.5.0_0    pytorch-nightly
[conda] pytorch-cuda              11.7                 h67b0de4_2    pytorch-nightly
[conda] pytorch-mutex             1.0                        cuda    pytorch-nightly
[conda] torchaudio                2.0.0.dev20230105      py39_cu117    pytorch-nightly
[conda] torchtriton               2.0.0+0d7e753227            py39    pytorch-nightly
[conda] torchvision               0.15.0.dev20230105      py39_cu117    pytorch-nightly
```