ImputeSuperIndividuals may to impute for all super-individuals when some are used in multiple strata. #283
Description
The issue is that the Individual column of the SuperIndividualsData can have duplicates if individuals are used across multiple strata. The ImputeSuperIndividuals function may register that at least one of the rows with identical Individual has the data to impute, but actually selecting that value fails if the first of those rows has missing value.
The solution is to introduce a unique ID named StratumLayerIndividual, which is a concatenation of Stratum, Layer and Individual, and use this in the ImputeSuperIndividuals function. This is a non-backwardly compatible change, as the order of the table may change by using the new StratumLayerIndividual, resulting in a different seed effect.
Scheduled for StoX 4.0.0.