message: Fix createImageBitmap with null alphaMode
diff: @@ -209,7 +209,8 @@ export class ImageResource extends BaseImageResource
  .then((blob) => createImageBitmap(blob,
  0, 0, source.width, source.height,
  {
  - premultiplyAlpha: this.alphaMode === ALPHA_MODES.UNPACK ? 'premultiply' : 'none',
  + premultiplyAlpha: this.alphaMode === null || this.alphaMode === ALPHA_MODES.UNPACK
  + ? 'premultiply' : 'none',
  }))
  .then((bitmap: ImageBitmap) =>
  {
  