Fix the request count for a pagination loop

Your client pages through a REST API with a loop that stops when a page comes back with fewer than per_page items. The loop passed a smoke test against 250 items. Before it ships, you want to compare its cost with a loop that reads the API's own total.

An assistant wrote page_request_counts(total_items, per_page) to count the requests each loop makes. It is in the editor. It has a bug. Find it and fix it.

Input and output:

• total_items: how many items the collection holds.
• per_page: how many items a full page holds.
• Return [contract_calls, short_page_calls], or [] when the input is invalid.

Rules the tests check:

• The input is invalid when per_page is 0 or less, or total_items is less than 0.
• contract_calls is the number of pages needed to hold total_items, rounded up, and at least 1: you always make the first call, even for an empty collection.
• short_page_calls is how many calls the short page loop makes. It requests pages 1, 2, 3 and so on, and stops right after the first page that holds fewer than per_page items. An empty page counts as one of those.