nxinspect crashes when cannot resolve the link to an internal field

[jkotan]

The issue is similar to #12 but for internal links i.e. when a target of internal link is not created
nxinspect crashes e.g.

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 4529, in __getitem__
    node = node.entries[name]
           ~~~~~~~~~~~~^^^^^^
KeyError: 'target'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 5270, in __getattr__
    return getattr(self.nxlink, name)
                   ^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 5371, in nxlink
    self._link = self.internal_link
                 ^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 5403, in internal_link
    return self.nxroot[self._target]
           ~~~~~~~~~~~^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 4531, in __getitem__
    raise NeXusError("Invalid path")
nexusformat.nexus.tree.NeXusError: Invalid path

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/jkotan/testinst/local/bin/nxinspect", line 8, in <module>
    sys.exit(main())
             ^^^^^^
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/scripts/nxinspect.py", line 75, in main
    validate_file(filename, path=path, definitions=definitions)
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/validate.py", line 953, in validate_file
    validator.validate(path)
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/validate.py", line 926, in validate
    validator.validate(item, indent=indent)
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/validate.py", line 576, in validate
    field_validator.validate(tag, item, parent=self, indent=indent)
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/validate.py", line 840, in validate
    self.check_type(field, tag['@type'])
  File "/home/jkotan/testinst/local/lib/python3.11/dist-packages/nxvalidate/validate.py", line 613, in check_type
    if is_valid_float(field.dtype):
                      ^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/nexusformat/nexus/tree.py", line 5272, in __getattr__
    raise NeXusError(f"Cannot resolve the link to '{self._target}'")
nexusformat.nexus.tree.NeXusError: Cannot resolve the link to '/scan/sample_environment/mlz_stressihtf2_v2/He/parameters/target/value'

Instead, it would be nice to print an error, e.g. simialar one to the external links

This is a broken link to "/scan/sample_environment/mlz_stressihtf2_v2/He/parameters/target/value"