[FIX] l10n_es_aeat_mod303: Avoid negatives in fee to compensate

If the previous 303 report has remaining fee to compensate, and the
result of the report is positive and bigger than the fee to compensate,
when computing the current one, the constraint

  "The fee to compensate must be indicated as a positive number."

will raise always.

To avoid it, two changes have been done:

1. Only substract report result if it's of type C.
2. Nullify any possible result when it's less than 0.

Amendment of 4bd1c02

TT55245

l10n_es_aeat_mod303/models/mod303.py

@@ -519,18 +519,11 @@ def calculate(self):
                         - fields.Date.to_date(mod303.date_start)
                     ),
                 )
-                if prev_report and (
-                    prev_report.remaining_cuota_compensar > 0
-                    or prev_report.result_type == "C"
-                ):
-                    mod303.write(
-                        {
-                            "potential_cuota_compensar": (
-                                prev_report.remaining_cuota_compensar
-                                - prev_report.resultado_liquidacion
-                            ),
-                        }
-                    )
+                if prev_report.remaining_cuota_compensar > 0:
+                    amount = prev_report.remaining_cuota_compensar
+                    if prev_report.result_type == "C":
+                        amount -= prev_report.resultado_liquidacion
+                    mod303.potential_cuota_compensar = amount if amount > 0 else 0
             if mod303.return_last_period:
                 cuota_compensar = mod303.potential_cuota_compensar
             elif (
@@ -547,7 +540,6 @@ def calculate(self):
             else:
                 cuota_compensar = 0
             mod303.cuota_compensar = cuota_compensar
-
         return res
 
     def button_confirm(self):