[Product Reviews] Fix pagination

[magento-engcom-team]

During iteration product reviews the last element should return "null" for cursor value.

Steps to reproduce:

• Create 2 approved product reviews
• Start iterate over reviews with pagination size "1"
• call ProductReviews.getProductReviews method with gRPC UI
• with received cursor value from the previous call send new request to getProductReviews

Expected results:

• after 2nd call, cursor should have "null" value

Actual result:

• cursor is not null, send request with given cursor value to getProductReviews will return empty result

repo: https://github.com/magento/storefront-product-reviews-ce/

 

[magento-engcom-team]

The issue was exported from the internal JIRA. The link to the original JIRA issue: https://jira.corp.magento.com/browse/SFAPP-179