Bug 28664: Prevent refunds against void lines

Bug 28664: Prevent refunds against void lines

With the introduction of double entry accounting for VOID actions, we
need to add an additional filter to the 'Issue refund' button appearance

Test plan
1/ Add a debt
2/ Pay the debt
3/ Void the payment
4/ Confirm that with the patch applied the 'Issue refund' button doesn
not appear on the 'Void' accountline.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>