Fix bug in pays christmas computation
Fix bug in pays christmas computation

- if partner had several other contracts it crashed.

ecino/compassion-switzerland,CompassionCH/compassion-switzerland,ecino/compassion-switzerland,eicher31/compassion-switzerland,CompassionCH/compassion-switzerland,eicher31/compassion-switzerland,CompassionCH/compassion-switzerland,eicher31/compassion-switzerland,ecino/compassion-switzerland