Gets the current pixbuf which should be displayed.
The pixbuf might not be the same size as the animation itself (gdk_pixbuf_animation_get_width(), get_height).
This pixbuf should be displayed for get_delay_time milliseconds.
The caller of this function does not own a reference to the returned pixbuf; the returned pixbuf will become invalid when the iterator advances to the next frame, which may happen anytime you call advance.
Copy the pixbuf to keep it (don't just add a reference), as it may get recycled as you advance the iterator.
an animation iterator
the pixbuf to be displayed