[ticket/12220] Fix division by zero in search page with no results.

The page url parameter no longer exists in the pagination.on_page() method,
therefore the page url passed is being divided by 0 - the total number of
items. Since PAGE_NUMBER is assigned in generate_template_pagination(), this
separate assignment is no longer needed.

PHPBB3-12220
Merge pull request #2053 from prototech/ticket/12220

[ticket/12220] Fix division by zero in search page with no results.

* prototech/ticket/12220:
  [ticket/12220] Fix division by zero in search page with no results.