Repair count on stats announcement index

The count used to show the number of results _returned_, which would always
be 40 when looking at a result set >= 40 (40 per page). This fixes that.
Merge pull request #1582 from alphagov/fix-stats-announcement-index-count

Repair count on stats announcement index

The count used to show the number of results returned, which would always
be 40 when looking at a result set >= 40 (because 40 per page). This fixes that.

Story: https://www.pivotaltracker.com/story/show/73954532