possible race condition when using combination aggregats #8

When using normal aggregates it is guaranteed that the resulting emit will always have the same size, this means we can combine them without running into the issue that a upper level function receives data in different chunk size.

However combination functiosn do not guarantee this as when results on different terms come in in a wrong order (this can possibly happen!), the output can be the combination of more then 1 term.

This is a non issue if for normal aggregates but if a combination is on top of a combination there can be issues.

That said I'm not sure of a use case that would result in something like this but it's good to know the issue.