Fix crash passing an empty list to python openAuth() API

If passing a 'credtype' parameter which was an empty list
to the python openAuth() API, the 'credtype' field in
the virConnectAuth struct would not be initialized. This
lead to a crash when later trying to free that field.
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

python/libvirt-override.c

@@ -1820,6 +1820,7 @@ libvirt_virConnectOpenAuth(PyObject *self ATTRIBUTE_UNUSED, PyObject *args) {
     PyObject *pycredtype;
     virConnectAuth auth;
 
+    memset(&auth, 0, sizeof(auth));
     if (!PyArg_ParseTuple(args, (char *)"zOi:virConnectOpenAuth", &name, &pyauth, &flags))
         return NULL;