Bug 30848: Fix issue exposed by unit tests

Bug 30848: Fix issue exposed by unit tests

This patch changes the 'map' to a simple for loop so that we can easily
map multiple subfields to a field without overwriting the first previous
subfields in the structure.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit 6c381c4b22d30388f8e24966a6c6e7c78201dba3)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit 965e9856196a30520ffaea7cc99f7724f7b123d3)
Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>