dandi organize errors on zarr files

From the dandi-cli log:

```
>>> dandi organize path\\to\\data_1file_zarr

Traceback (most recent call last):
File "C:\Users\RBO\repos\mbo_utilities\.venv\Lib\site-packages\dandi\cli\base.py", line 126, in wrapper
return f(*args, **kwargs)
^^^^^^^^^^^^^^^^^^
File "C:\Users\RBO\repos\mbo_utilities\.venv\Lib\site-packages\dandi\cli\cmd_organize.py", line 112, in organize
organize(
File "C:\Users\RBO\repos\mbo_utilities\.venv\Lib\site-packages\dandi\organize.py", line 928, in organize
files_mode = detect_link_type(link_test_file, dandiset_path)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "C:\Users\RBO\repos\mbo_utilities\.venv\Lib\site-packages\dandi\organize.py", line 735, in detect_link_type
os.symlink(srcfile, destfile)
TypeError: symlink: src should be string, bytes or os.PathLike, not NoneType
```

This comes from [find_files](https://github.com/dandi/dandi-cli/blob/b8bb1de364e732d927e5e2c5bc86aaea6ba6acbb/dandi/organize.py#L841) incorrectly returning an empty list.

Manually organizing the dataset was done with @CodyCBakerPhD and uploaded to [DANDI Archive](https://dandiarchive.org/dandiset/001546/draft) for reference.

---

Side note: Since users can name zarr directories whatever they want, with or without file extensions, I think it's important to not use the extension as useful context to the contents of the file. This always confused me about zarr.