Bug Description

I know the main intent was to provide a replacement jpeg->webp but for an ecommerce I had to change the normal operation of the plugin (otherwise it would have been of little use since the images were almost all png with transparency)

Steps to reproduce

1. Add the filter

add_filter('webp_uploads_upload_image_mime_transforms', function() {
    return array(
        'image/png' => array( 'image/png', 'image/webp' ),
        'image/webp' => array( 'image/webp', 'image/png' ),
    );
});

2. Create a page and upload a bunch of png images
3. When you view that page and the fallback script is activated it tries to replace images jpg images only

Additional Context

• was previously discussed here Provide fallback JPEG images in frontend when WebP is not supported by the browser #360 (comment)