Update the JSD Satisfaction Survey trend reports to not indicate a "0" result for days customers have not submitted a survey

Our team's average rating is 5-stars, however the report shows 0s for days without data which indicates a different overall picture of the actual results. Most trend reports keep the line at the last reported data and not drop down to 0 on days without data, the only time I would expect to see it drop to 0 is if the customer survey reported a 0-star rating which isn't possible as the lowest customers can rate is a 1-star.

See https://answers.atlassian.com/questions/40001590/answers/40002156 for supporting screenshots.