API Response "total_cell_count" shows incorrect number of total cells in response

[otterbotter]

⚠️ Problem:

• total_cell_count in API response shows the wrong value when the number of cells is 1

Example of problematic response: https://openspending.org/api/3/cubes/b9d2af843f3a7ca223eea07fb608e62a:expenditure-time-series-v2/aggregate/?cut=amount_kind.amount_kind%3A%22Total%22%7Cfinancial_year.financial_year%3A2015&pagesize=10000

• Example of correct response:
  https://openspending.org/api/3/cubes/b9d2af843f3a7ca223eea07fb608e62a:expenditure-time-series-v2/aggregate/?cut=amount_kind.amount_kind%3A%22Total%22&drilldown=financial_year.financial_year%7Cbudget_phase.budget_phase%7Cvote_number.department%7Cprogramme_number.programme&pagesize=10000

In the first (problematic) response, the total_cell_count indicates 66859 which is equal to the total of cells included in all of the aggregations, but the number should be 1 because the length of the cells returned is 1.

In the second (correct) response, the total_cell_count indicates 2941 which is the number of cells returned in cells (which makes sense).