Fix for error in aggregate functions

[droberts-ctrlo]

This branch is taken straight from v2.5.5 tag

[droberts-ctrlo]

I didn't know which origin branch to do the PR for - obvs change it if you need to.

[abeverley]

Thanks Dave. Just to note that you could also have done this if you wanted:

$data->{$_->id} = $agg->get_field_value($_)->for_table
    foreach grep {$_->aggregate}, @{$records->columns_render};