Fix bug with mapping equivalences to flattened models.
Fix bug with mapping equivalences to flattened models.

nickerso/libcellml,hsorby/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,cellml/libcellml,cellml/libcellml,nickerso/libcellml,nickerso/libcellml,hsorby/libcellml,hsorby/libcellml,hsorby/libcellml