Support all image types (not only TYPE_3BYTE_BGR and TYPE_4BYTE_ABGR).

The fast implementation to read the image's pixels into a byte array,
which is currently used, works only for the image types TYPE_3BYTE_BGR
and TYPE_4BYTE_ABGR.

For all other image types (which are used very rarely), the pixels will
be read via the slow BufferedImage.getRGB(..) method.