fix: label value formatting on non-XY charts

[meronz]

This is done to correctly show the tooltip values.

Bug info

I fixed it by checking the undefined values in the blazor_apexcharts.js wrapper. Not sure if this is the correct way of doing this.

Screenshot of the exception:

 Steps to reproduce:

• Create a chart with FormatYAxisLabel set. Full example:

  <ApexChart TItem="TestItem"
                     Title="SeriesType.Pie"
                     FormatYAxisLabel="MyFormatYAxisLabel">
  
              <ApexPointSeries TItem="TestItem"
                               Items="Items"
                               Name="Gross Value"
                               SeriesType="@type"
                               XValue="@(e => e.Id)"
                               YValue="@(e => e.Value)"/>
  
          </ApexChart>
  
  @code
  {
      public record TestItem(string Id, decimal? Value);
  
      public TestItem[] Items => new[]
      {
          new TestItem("1", 1.0m),
          new TestItem("2", 2.123m),
          new TestItem("3", 3.123m),
          new TestItem("4", null),
          new TestItem("5", 5.123m),
      };
  
      private string MyFormatYAxisLabel(decimal arg)
      {
          return arg.ToString("c"); // should format to euros
      }
  }