Bug 21641: (follow-up) Address wrong call method

Bug 21641: (follow-up) Address wrong call method

This patch substitutes C4::Accounts->getnextacctno for
C4::Accounts::getnextacctno since getnextacctno is only expecting to be
passed a borrowernumber

Signed-off-by: Alex Buckley <alexbuckley@catalyst.net.nz>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 4858c4f736d366701fa6a3f1def2727dd85c70ce)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>