Queries the Pixbuf that a pixbuf loader is currently creating.
In general it only makes sense to call this function after the [signal
area_prepared] signal has been emitted by the loader; this
means that enough data has been read to know the size of the image that will be allocated.
If the loader has not received enough data via write, then this function returns `NULL`.
The returned pixbuf will be the same in all future calls to the loader, so if you want to keep using it, you should acquire a reference to it.
Additionally, if the loader is an animation, it will return the "static image" of the animation (see get_static_image).
A pixbuf loader.
The pixbuf that the loader is creating