Even bandsCount >= 5 in DataTileSource not working correctly

[fabry24]

Describe the bug Using even bandsCount >= 6 in DataTileSource generates incorrect output, when using last band as alpha channel. What we try to do

1. Set layer style to show RGBA
2. {color: ["color",["band", 4],["band", 3],["band", 2],["/", ["band", bands.length + 1], 255]]}
3. Ask for 5 bands from titiler - you'll get 6bands (5bands + alpha) as output
4. Set DataTileSource to work with 6 bands (5 + alpha)
5. Alpha mask is not working correctly
6. To fix this behavior we generated ol/DataTile with one more dimension, when working with even bandsCount:

To Reproduce Steps to reproduce the behavior:

1. Change value of totalBandsCount (row: 24) directly to bandsCount (In this example it is 6).

Example https://codesandbox.io/s/numpytile-forked-e279im

[mike-000]

I also encounter this with a 5 band GeoTIFF (returning 6 bands including the alpha). The workaround there is to explicitly specify the bands and duplicate one of them:

  sources: [
    {
      nodata: 0,
      bands; [1, 2, 3, 4, 5, 5],
      url: 'xxxx.tif',
    },
  ],