Fix registration hooks (#87369)
There is a bug in the implementation of the registration hooks introduced in https://github.com/pytorch/pytorch/pull/86148 whereby if the hook returns a tensor, then the short circuiting logic:
```
value = hook(self, name, value) or value
```
Raises an exception
```
RuntimeError: Boolean value of Tensor with more than one value is ambiguous
```
Fixing the logic so that it only checks to see if the value is `None` before overriding
Fixes #85837
CC: @albanD @jbschlosser
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87369
Approved by: https://github.com/albanD
