WebP should not use lossless encoding for (most) thumbnailing

[discomrade]

The WebP option for thumbnails has the webp:lossless option enabled. However, if an image is being downscaled or upscaled to make a thumbnail, there is no point using a lossless file encoding because the data is already changed. This would only make sense if a lossless data type (e.g. PNG, GIF) is remaining the exact same size in its thumbnail (e.g. if it's smaller than the thumbnail size, like an icon or sprite, and the fit setting doesn't upsize it). For all other cases, this will just ignore the admin's quality option and use a lossless encoding which creates pointlessly large filesizes.

note: I've only tested with ImageMagick, I'm not sure how GD works.