Error responses missing `result_type`

[benthecarman]

When parsing error responses from a NWC event from alby I'll get something like

{
  "error": {
    "code": "INTERNAL",
    "message": "Something went wrong while paying invoice: not enough balance. Make sure you have at least 1% reserved for potential fees"
  }
}

the error responses are supposed to include result_type so we know which method was used for this error.