initialize nb_of_transactions_2_4 and control_sum_2_5 with Default value

When we export File and if pain_flavor == pain.001.001.02
we are getting the error for nb_of_transactions_2_4 is not define

as it is not initialized before if condition.
from file account_banking_pain_base/banking_export_pain.py

Migratefrom Launchpad to github
https://code.launchpad.net/~ruchir.shukla/banking-addons/banking-addons-fix-1334526/+merge/224554