Use entry amount when amount is missing from details

Closes #14904
(grafted from d7c4e8ae89e4b289fb5cf244946787793454ec3e)

--HG--
branch : 8.0

modules/account_statement_sepa/account.py

@@ -73,7 +73,8 @@ class StatementImport(metaclass=PoolMeta):
         return statement
 
     def _camt_amount(self, entry, detail=None):
-        if detail is not None:
+        if (detail is not None
+                and detail.find('./{*}AmtDtls/{*}TxAmt/{*}Amt') is not None):
             amount = Decimal(detail.findtext('./{*}AmtDtls/{*}TxAmt/{*}Amt'))
         else:
             amount = Decimal(entry.findtext('./{*}Amt'))