/jobs/failed showing wrong ending job # on header

[palfvin]

When listing failing jobs, the upper end of the job range shown in the header is one higher than it should be, due to the header referencing the following:

def failure_end_at
  if failure_start_at + failure_per_page > failure_size
    failure_size
  else
    failure_start_at + failure_per_page
  end
end

Both the pagination and non-pagination cases appear wrong.

Note: This all assumes that the convention of addressing jobs starting with zero is intentional.