Bug 29385: Catch register_id for payments against fees

Bug 29385: Catch register_id for payments against fees

This patch refactors the pay method in SIP FeePayment such that we
consistently pass parameters to both invocations of Koha::Account->pay.

It ensure the missing cash_register definition is passed when a set of
account lines to pay is defined.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>