Multi-category sorting misbehaves with missing categories

Originally reported in https://github.com/plotly/plotly.py/issues/1491.

There seems to a multi-category sorting bug that wasn't fixed by #3362.

CodePen: https://codepen.io/jonmmease/pen/VNeEqq?editors=1010

var fig = {
  "data": [
    {
      "name": "Fruits",
      "type": "bar",
      "x": [
        [
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2018,
          2018,
          2018,
          2018
        ],
        [
          4,
          5,
          6,
          8,
          9,
          10,
          11,
          12,
          1,
          2,
          3,
          4
        ]
      ],
      "y": [
        57246.0,
        1587.0,
        63189.0,
        30680.0,
        26071.0,
        117519.0,
        27519.0,
        42643.0,
        8559.0,
        22355.0,
        59363.0,
        62955.0
      ]
    },
    {
      "name": "Price",
      "type": "scatter",
      "x": [
        [
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2017,
          2018,
          2018,
          2018,
          2018
        ],
        [
          4,
          5,
          6,
          8,
          9,
          10,
          11,
          12,
          1,
          2,
          3,
          4
        ]
      ],
      "y": [
        0.22991999,
        0.27284184,
        0.18438336,
        0.24866362,
        0.18280848,
        0.19382398,
        0.17268069,
        0.18802617,
        0.17560463,
        0.13415343,
        0.14773512,
        0.31319196
      ],
      "yaxis": "y2"
    }
  ],
  "layout": {
    "height": 600,
    "showlegend": true,
    "yaxis": {
      "showgrid": true,
      "title": {
        "text": "Fruits volume"
      }
    },
    "yaxis2": {
      "anchor": "x",
      "overlaying": "y",
      "showgrid": false,
      "side": "right",
      "title": {
        "text": "Price per unit"
      }
    }
  }
}

Plotly.newPlot('myDiv', fig, {showSendToCloud: true});

The problem is that in the second multi-category (2018), the 4 is sorted before 1, 2, 3 even though they are specified in ascending sorted order.

As noted in https://github.com/plotly/plotly.py/issues/1491, this seems to happen for categories that are not present in the first multi-category (2017).

Riproduci il comportamento utilizzando l’esempio CodePen fornito e la configurazione di Plotly.newPlot, concentrandoti sull’ordinamento di un asse con più categorie quando una categoria compare solo nel gruppo successivo. Confronta l’ordine visualizzato con l’ordine crescente specificato; il lavoro è completato quando la seconda categoria multipla viene ordinata come 1, 2, 3, 4, preservando il comportamento riportato nell’esempio.