fix import-no-init

[comhar]

fixes #815

When running the xtra notebook locally I'm getting the following error:

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
Cell In[75], line 1
----> 1 m = import_no_init('fastcore.basics')
      2 test_eq(m.__name__, 'fastcore.basics')
      3 assert hasattr(m, 'store_attr')
      4 

Cell In[74], line 7, in import_no_init(name)
      3     from importlib.machinery import PathFinder
      4     import importlib.util as iu
      5     parts = name.split('.')
      6     spec = PathFinder.find_spec(parts[0])
----> 7     path = Path(spec.origin)
      8     if len(parts)>1: path = path.parent.joinpath(*parts[1:]).with_suffix('.py')
      9     spec = iu.spec_from_file_location(name, path)
     10     mod = iu.module_from_spec(spec)

AttributeError: 'NoneType' object has no attribute 'origin'

On my machine fastcore is an editable install and PathFinder.find_spec can't find it.
iu.find_spec can find it.

This pr makes the following change.

spec = PathFinder.find_spec(parts[0])

to

spec = PathFinder.find_spec(parts[0]) or iu.find_spec(parts[0]).