fix: Fill totals with correct amount of zeroes for empty reports

[aragaer]

In current implementation balancesheet and balancesheetequity result in incorrect CSV output if one of the subreports is empty -- the "total" row for that subreport contains only "total" field and nothing else.

The solution is to know in advance the number of columns and fill total with zeroes if subreport is empty.

This might make #588 unneeded since now subreport's totals is never empty.

[simonmichael]

Looks good, thank you!