Get the right mandate when creating voucher.

cotisations/utils.py

@@ -99,7 +99,7 @@ def send_mail_invoice(invoice):
 
 def send_mail_voucher(invoice):
     """Creates a voucher from an invoice and sends it by email to the client"""
-    president = Mandate.get_mandate().president
+    president = Mandate.get_mandate(invoice.date).president
     ctx = {
         'asso_name': AssoOption.get_cached_value('name'),
         'pres_name': ' '.join([president.name, president.surname]),

cotisations/views.py

@@ -1068,7 +1068,7 @@ def voucher_pdf(request, invoice, **_kwargs):
             _("Could not find a voucher for that invoice.")
         )
         return redirect(reverse('cotisations:index'))
-    president = Mandate.get_mandate().president
+    president = Mandate.get_mandate(invoice.date).president
     return render_voucher(request, {
         'asso_name': AssoOption.get_cached_value('name'),
         'pres_name': ' '.join([president.name, president.surname]),