Automaticly replace missing Portraits for ddragon

[LogicalOverflow]

From time to time (on 7.1.1 it happens for anivia), the champion portraits are completely light blue images. This happens when the ddragon does not have/provide the correct one, but the placeholder image. Maybe it would be nice to fall back to a previous version if this happens. Checking if the image is a placeholder could be done by checking if it is just the one color of the placeholder image.