core dump when progress callback raises an Exception

[mklein-de]

How to reproduce:

!/usr/bin/env python3

import sane

sane.init()

def progress(*args):
    print(args)
    1/0
                                                                                                                                                                  
sane.open(sane.get_devices()[0][0]).scan(progress=progress)

core dump is caused by Py_DECREF(result); with a NULL result