do close pixbuf loaders if loading is unsuccessful

[mfrasca]

I'm running unit tests, and I'm having the software refer to pictures that do not exist. it should not be a problem, I receive an error message, that's fine. but after the program closes, the Gdk system complains about not closing pixbuf loaders.

Actual behaviour

(nosetests:8086): GdkPixbuf-WARNING **: GdkPixbufLoader finalized without calling gdk_pixbuf_loader_close() - this is not allowed. You must explicitly end the data stream to the loader before dropping the last reference.