No error handling when taking a quiz

[brianhogg]

Reproduction Steps

1. Start a quiz as a student
2. Disconnect from the internet
3. Attempt to answer the question

The same thing would be seen if there's a temporary server error rather than a disconnect from the internet.

Expected Behavior

Error message is shown and student can try again when internet reconnects.

Actual Behavior

Loading spinner continues to show, student is not able to retry.

This issue has be recreated:

• [x] Locally
• [x] On a staging site
• [x] On a production website
• [x] With only LifterLMS and a default theme