VID-1739

I see, this bumps the delay index for this next try.  Maybe you should just pass $delayIndex+1 when starting this next try in uploadBestThumbnail:

  $task->call( 'retryThumbUpload', $this->getDestinationTitle(), $delayIndex+1 );

That way the bump happens where delayIndex is used which I think makes it a little easier to understand.