[Editor] Show Answer setting cannot be switched back to "Finished" after first edit

[jristau1984]

Steps to Reproduce:

1. Edit a Problem
2. Change the show answer setting from "Finished (Default) to "Attempted"
3. Save and Publish.
4. Go back to the problem and click to edit.
5. Note that Show answer is set to "Attempted"

Expected Behavior:
When “Show Answer” setting is changed, it should allow to change the setting back to the "Finished (Default)" setting

Actual Behavior:
When “Show Answer” setting is changed, it does not allow to change the setting back to the "Finished (Default)" setting

Impact:

The course teams are unable to change the Show Answer setting back to their desired setting. They will need to create a new problem to overcome this hurdle which is not the solution in a live course because it will impact learners' submissions and will result in losing the score who have already answered.