Do not set unit price or quantity if empty

The unit price or the quantity of the credit note line should not be updated
if the value from the complain invoice line is None as it means we must use
the original one.

issue9497
review290651002

complaint.py

@@ -498,9 +498,11 @@ class Action(ModelSQL, ModelView):
                 if self.invoice_lines:
                     invoice_lines = [l.line for l in self.invoice_lines]
                     line2qty = {l.line: l.quantity
-                        for l in self.invoice_lines}
+                        for l in self.invoice_lines
+                        if l.quantity is not None}
                     line2price = {l.line: l.unit_price
-                        for l in self.invoice_lines}
+                        for l in self.invoice_lines
+                        if l.unit_price is not None}
                 else:
                     invoice_lines = invoice.lines
             elif isinstance(self.complaint.origin, Line):