Skip/handle incomplete questions during exercise generation in publish

[sentry]

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Sentry Issue: STUDIO-HX6

ValidationError: 1 validation error for ChoiceInteraction
answers
  List should have at least 1 item after validation, not 0 [type=too_short, input_value=[], input_type=list]
    For further information visit https://errors.pydantic.dev/2.11/v/too_short
(8 additional frame(s) were not displayed)
...
  File "contentcuration/utils/publish.py", line 360, in recurse_nodes
    generator.create_exercise_archive()
  File "contentcuration/utils/assessment/base.py", line 393, in create_exercise_archive
    self.process_assessment_item(question)
  File "contentcuration/utils/assessment/base.py", line 344, in process_assessment_item
    filepath, file_content = self.create_assessment_item(assessment_item, context)
  File "contentcuration/utils/assessment/qti/archive.py", line 184, in create_assessment_item
    ) = self._create_choice_interaction_and_response(processed_data)
  File "contentcuration/utils/assessment/qti/archive.py", line 122, in _create_choice_interaction_and_response
    interaction = ChoiceInteraction(

[rtibbles]

This error has not recurred on Sentry in 25 days, so I think this has been fixed in the course of other fixes and updates.