zmq_msg_send not working

Hi!

zmq_msg_send seems to have a strange problem. I get the following error when I try to use it:
ZMQ::LibZMQ3::Message: Invalid ZMQ::LibZMQ3::Message object was passed to mg_find

see the test case in this commit (copied from 100_basic.t, test #3 works (using zmq_sendmsg), but #4 fails when using zmq_msg_send.

Sorry, my C is nonexistent, so I have no idea what might be the problem...