fix: support decollate for numpy scalars (#8470)

Fixes #8471

### Description

This PR supports numpy scalars (e.g. in the form of `np.array(1)` ) in
the `decollate_batch` function (fix issue
#8471).

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [x] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [x] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

---------

Signed-off-by: Arthur Dujardin <arthurdujardin.dev@gmail.com>
Co-authored-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>
Co-authored-by: Eric Kerfoot <17726042+ericspod@users.noreply.github.com>

Author: 3 people

monai/data/utils.py

@@ -597,11 +597,12 @@ def decollate_batch(batch, detach: bool = True, pad=True, fill_value=None):
         type(batch).__module__ == "numpy" and not isinstance(batch, Iterable)
     ):
         return batch
+    # if scalar tensor/array, return the item itself.
+    if getattr(batch, "ndim", -1) == 0 and hasattr(batch, "item"):
+        return batch.item() if detach else batch
     if isinstance(batch, torch.Tensor):
         if detach:
             batch = batch.detach()
-        if batch.ndim == 0:
-            return batch.item() if detach else batch
         out_list = torch.unbind(batch, dim=0)
         # if of type MetaObj, decollate the metadata
         if isinstance(batch, MetaObj):