Deprecated warning with incomplete quiz attempts

[brianhogg]

Reproduction Steps

1. Turn on debugging display on the site
2. Start taking a quiz in a course
3. Refresh the page to exit the quiz before completed

Expected Behavior

No warning is displayed

Actual Behavior

Warning is displayed in the attempts dropdown:

and when you select that attempt in the dropdown:

Error Messages / Logs

PHP Deprecated:  round(): Passing null to parameter #1 ($num) of type int|float is deprecated in .../wp-content/plugins/lifterlms/templates/quiz/results.php on line 75

PHP Deprecated:  strtotime(): Passing null to parameter #1 ($datetime) of type string is deprecated in .../wp-content/plugins/lifterlms/includes/models/model.llms.quiz.attempt.php on line 344

This issue has be recreated:

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