[14.0][FIX] l10n_it_ricevute_bancarie: avoid loosing reference to lines partner
[14.0][FIX] l10n_it_ricevute_bancarie: avoid loosing reference to lines partner

Itroduce a check on the array because when no line has a .due_cost_line, the actions modified deleted the partner's reference in all the lines

OCA/l10n-italy,OCA/l10n-italy,OCA/l10n-italy