Skip generating of webp assets for absolute pathed images

I've added a patch that skips webp generation of images that are absolute pathed.

I've updated this patch to use the UrlHelper::isExternal() method for checking the path. We check if the image path is external before WebP processing gets a handle of it. This avoids Webp having issues and giving errors like "Could not generate image resource" errors due to it not knowing how to deal with external image paths.

I messed up the last uploaded patch. I uploaded a new patch that includes the UrlHelper::isExternal() check of the image path. This way, Webp will skip the image if the image path is external, since it doesn't know what to do with external pathed images.