Fix chart crashing when max is defined but ticks are empty

[KurtPreston]

If tick size is 0, and a max is defined without min, Chart.js would crash with:

react_devtools_backend.js:4049 Uncaught TypeError: Cannot read property 'value' of undefined TypeError: Cannot read property 'value' of undefined
    at generateTicks$1 (chart.esm.js:9359)
    at LinearScale.buildTicks (chart.esm.js:9461)
    at LinearScale.update (chart.esm.js:3810)
    at fitBoxes (chart.esm.js:2852)
    at Object.update (chart.esm.js:2988)
    at Chart._updateLayout (chart.esm.js:5657)
    at Chart.update (chart.esm.js:5638)
    at updateChart (index.modern.js:137)
    at index.modern.js:157

This adds an extra check to prevent ticks[ticks.length - 1] from erroring.

[etimberg]

The change looks fine. is it possible to write a test case for this?

[KurtPreston]

@etimberg I've pushed an update with a new spec.

Without the code change, the following error is thrown when the spec is executing:

        TypeError: Cannot read property 'value' of undefined
            at generateTicks$1 (src/chart.js:11970:46)
            at LinearScale.buildTicks (src/chart.js:12072:19)
            at LinearScale.update (src/chart.js:5035:19)
            at fitBoxes (src/chart.js:2144:9)
            at Object.update (src/chart.js:2280:5)
            at Chart._updateLayout (src/chart.js:6889:13)
            at Chart.update (src/chart.js:6870:8)
            at new Chart (src/chart.js:6626:10)
            at _acquireChart (node_modules/chartjs-test-utils/dist/chartjs-test-utils.js:601:13 <- test/index.js:606:15)
            at acquireChart (node_modules/chartjs-test-utils/dist/chartjs-test-utils.js:1136:15 <- test/index.js:1141:17)

[kurkle]

There seems to be another related case:

    var chart = window.acquireChart({
      type: 'line',
      data: {
        datasets: [{
          data: [200]
        }],
      },
      options: {
        scales: {
          y: {
            min: 250
          }
        }
      }
    });

    expect(chart.scales.y.min).toBe(250);

    RangeError: minimumFractionDigits value is out of range.
      at new NumberFormat (<anonymous>)
       at getNumberFormat (src/chart.js:2822:17)
       at formatNumber (src/chart.js:2828:10)
       at LinearScale.numeric (src/chart.js:4589:12)
       at callback (src/chart.js:802:15)
       at LinearScale.generateTickLabels (src/chart.js:5145:20)
       at LinearScale._convertTicksToLabels (src/chart.js:5298:8)
       at LinearScale.update (src/chart.js:5055:8)
       at fitBoxes (src/chart.js:2144:9)
       at Object.update (src/chart.js:2280:5)

Both cases are fixed by making sure min <= max in the getMinMax of core.scale

    // Make sure min <= max when only min or max is defined by user and the data is outside that range
    min = maxDefined && min > max ? max : min;
    max = minDefined && min > max ? min : max;

    return {
      min: finiteOrDefault(min, finiteOrDefault(max, min)),
      max: finiteOrDefault(max, finiteOrDefault(min, max))
    };

[kurkle]

So, my question is, are you willing to fix the other case here too, or should it be handled separately?
I think the length check should be included anyway.

[etimberg]

@kurkle had a good comment. I think it'd be good to address the two cases together