[image] Fix a memory leak in free_image()

image_set_cmdline() strdup()s cmdline, which free_image() doesn't
clean up.

Signed-off-by: Piotr Jaroszyński <p.jaroszynski@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/image.c

 static void free_image ( struct refcnt *refcnt ) {
 	struct image *image = container_of ( refcnt, struct image, refcnt );
 
+	free ( image->cmdline );
 	uri_put ( image->uri );
 	ufree ( image->data );
 	image_put ( image->replacement );