Better error handling for Browser

[mostlyobvious]

Consider following scenario:

• broken events JSON from backend (i.e. missing timestamp key in metadata, i.e. due to misconfigured Event class like Ruby Event Store Browser not loading events because of nil error #762)

  {
    "data": [
        {
            "id": "c6fcd01d-b708-46a7-b712-18783cc6e880",
            "type": "events",
            "attributes": {
                "event_type": "DummyEvent",
                "data": {
                    "some_integer_attribute": 42,
                    "some_string_attribute": "foobar",
                    "some_float_attribute": 3.14
                },
                "metadata": {},
                "correlation_stream_name": "$by_correlation_id_469904c5-46ee-43a3-857f-16a455cfe337",
                "causation_stream_name": "$by_causation_id_c6fcd01d-b708-46a7-b712-18783cc6e880",
                "type_stream_name": "$by_type_DummyEvent",
                "parent_event_id": null
            }
        }
  ]

• event decoder expecting timestamp to be present and generating Err on lack of it

  eventDecoder_ : Decoder Event
  eventDecoder_ =
      succeed Event
          |> requiredAt [ "attributes", "event_type" ] string
          |> requiredAt [ "id" ] string
          |> requiredAt [ "attributes", "metadata", "timestamp" ] Iso8601.decoder
          |> requiredAt [ "attributes", "data" ] (value |> Json.Decode.map (encode 2))
          |> requiredAt [ "attributes", "metadata" ] (value |> Json.Decode.map (encode 2))
          |> optionalAt [ "attributes", "correlation_stream_name" ] (maybe string) Nothing
          |> optionalAt [ "attributes", "causation_stream_name" ] (maybe string) Nothing
          |> requiredAt [ "attributes", "type_stream_name" ] string
          |> optionalAt [ "attributes", "parent_event_id" ] (maybe string) Nothing

  ▾GotShowStreamMsg EventsFetched …
  ▾0 = Err BadBody …
   0 = "Problem with the value at json.data[0].attributes.metadata:\n\n {}\n\nExpecting an OBJECT with a field named `timestamp`"
  

• handling of Err in update

          EventsFetched (Err errorMessage) ->
            ( model, Cmd.none )

• view on initial data being optimistic

  renderResults baseUrl events =
     case events of
          [] ->
              p [ class "results__empty" ] [ text "No items" ]
  

We end up with empty page suggesting no items like no error ever happened. Backend logs show to clue either -- all is good there.