Links to inacitve items raise `DoorstopError` instead of `DoorstopInfo`

[opt12]

Using version 3.0.2 on windows with Python 3.11

observed beahvior:
When running the doorstop command on a sample document tree, with some links to inactive items, the program stops with a DoorstopError:

checking item REQ-B-001...
ERROR: no item with UID: REQ-A-018

expected behavior:
The program should issue a DoorstopInfo saying: linked to inactive item: REQ-A-018

Source (from ItemValidator._get_issues_tree() in file item_validator.py):

            else:
                # check the parent item
                if not parent.active:
                    msg = "linked to inactive item: {}".format(parent)
                    yield DoorstopInfo(msg)

[opt12]

Additional Info
When using the -Z- option (i. e. "require child (reverse) links from every document") and it happens to hit an inactive document having links to a parent, the program crashes after a DoorstopWarning:

WARNING: no item with UID: REQ-C-038
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Scripts\doorstop.exe\__main__.py", line 7, in <module>
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\cli\main.py", line 179, in main
    success = function(args, os.getcwd(), parser.error)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\cli\commands.py", line 97, in run
    valid = tree.validate(skip=args.skip, item_hook=cycle_tracker)
            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\base.py", line 138, in validate
    for issue in self.get_issues(
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\tree.py", line 484, in get_issues
    for issue in chain(
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\document.py", line 867, in get_issues
    for issue in chain(
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\validators\item_validator.py", line 97, in get_issues
    yield from self._get_issues_both(item, item.document, item.tree, skip)
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\validators\item_validator.py", line 215, in _get_issues_both
    prefix = [item.document.prefix for item in items]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\validators\item_validator.py", line 215, in <listcomp>
    prefix = [item.document.prefix for item in items]
              ^^^^^^^^^^^^^
  File "C:\Users\FEckstein\AppData\Local\miniconda3\envs\py311\Lib\site-packages\doorstop\core\item.py", line 941, in __getattr__
    return self.__getattribute__(name)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'UnknownItem' object has no attribute 'document'