Participant non-answer is not displayed

[timloudon]

Describe the bug
If a participant does not answer a question their non-answer is not displayed on the QuestionMarker component.

To Reproduce
Steps to reproduce the behaviour:

1. Go to quiz.coffee
2. Create a quiz with questions
3. Participant fails to answer a question
4. See that a participant's non-answer is not displayed

Expected behaviour
The quiz host should see that a contestant has failed to submit an answer.

Actual behaviour
The quiz host cannot see that a contestant has not answered a question.