Victor Stinner's patches to check the return result of PyLong_Ssize_t

reviewed by Amaury
diff --git a/Modules/_struct.c b/Modules/_struct.c
index 078c3a5..30feaa6 100644
--- a/Modules/_struct.c
+++ b/Modules/_struct.c
@@ -1755,6 +1755,8 @@
 
 	/* Extract the offset from the first argument */
 	offset = PyInt_AsSsize_t(PyTuple_GET_ITEM(args, 1));
+	if (offset == -1 && PyErr_Occurred())
+		return NULL;
 
 	/* Support negative offsets. */
 	if (offset < 0)