Bug 35989: (QA follow-up) Add test and limit variable scope

Bug 35989: (QA follow-up) Add test and limit variable scope

Before this patch if a record had a 751 and a 781 you could have fields repeated.
This patch reduces the scope of the fields to subdivision variable as it is only used in processing 7xx
fields and should not be shared between fields.

I also add unit tests

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>