gh-153803: Raise ResponseError for a malformed struct in xmlrpc.client

[tonghuaroot]

Unmarshaller.end_struct iterates stacked name/value items in pairs. A <member> missing its <value> leaves an odd item count, so items[i+1] raises a raw IndexError. Guard with len(items) % 2 and raise ResponseError, matching the sibling checks at lines 640 and 663.

• Issue: xmlrpc.client.loads raises IndexError on a malformed struct #153803