Exclude 0-point quizzes from total grade calculation.

[dominiquemariano]

Reproduction Steps

1. Create a new quiz inside a new course inside a new lesson.
2. Add a single question on that quiz. Make sure that that question has a non-zero point (e.g., 1 point)
3. Create another quiz inside the same course on a different lesson. Make sure that that question has a zero points (i.e., 0 point)
4. Enroll to the course.
5. Take the first quiz and pass it so that your grade is 100%.
6. Take the second quiz.

Expected Behavior

The total grade should still be 100%.

Actual Behavior

The total grade should still be 50%.

This issue has be recreated:

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