Fix column mapping for resultSortedOn()
Fix column mapping for resultSortedOn()

previously we were using the column mapping of the child subtree,
however that can be wrong for the result when new columns are added
(e.g. by using COUNT()). Somehow this was masked in previous versions of
the column mapping.

Buchhold/QLever,Buchhold/QLever,Buchhold/QLever,Buchhold/QLever,Buchhold/QLever