[IMP] add warning message if nothing done

wizard/account_bank_statement_import.py

@@ -33,3 +33,8 @@ class AccountStatementImport(models.TransientModel):
             )
             self.import_single_statement(single_statement_data, result)
         logger.debug("result=%s", result)
+        if not result["statement_ids"]:
+            logger.warning(
+                "You have already imported this file, or this file "
+                "only contains already imported transactions."
+            )