Returns the number of states for taxon `i', character `j'.
If `j' is equal to or greater than the number of characters for taxon `i', returns UINT_MAX. If there is missing data, the return value is 0, otherwise a positive integer will be returned. An alternative is to use the function GetInternalRepresentation to obtain a vector of all states, and the size of that vector could be used to determine both the number and the identity of the states. If no data was stored for the taxon having index i in the UNALIGNED block, a NxsUnalignedBlock::NxsX_NoDataForTaxon exception is thrown.