slapos_accounting: Update Price assertion constraint

   We do expect that all trade conditions be attached to a business process, so for manual accounting
   the condition changed.

    Se would like to skip consistency check if the invoice isn't automated (ledger) and has no lines,
   otherwise this consistency check should still apply as usual.

master/bt5/slapos_accounting/SkinTemplateItem/portal_skins/slapos_accounting/SaleInvoiceTransaction_isTotalPriceEqualAccounting.py

 invoice = context
 
-specialise = context.getSpecialiseValue(portal_type='Sale Trade Condition')
-if specialise is None or specialise.getSpecialiseValue() is None:
-  if not len(invoice.objectValues(portal_type="Invoice Line")):
-    # The trade model don't applies if the Trade Condition isn't attached to
-    # A business process
-    return True
-
-
+if invoice.getLedger() != 'automated' and \
+    not len(invoice.objectValues(portal_type="Invoice Line")):
+  # Non automated invoices can be used w/o Invoice Lines for
+  # the most part.
+  return True
 
 total_price = invoice.getTotalPrice()
 if invoice.getTotalPrice() < 0: