Fix the segfault when over-sized message is rejected.

The in_progress message inside of decoder was left
uninitialised in such a case.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>

src/decoder.cpp

@@ -92,6 +92,8 @@ bool zmq::decoder_t::eight_byte_size_ready ()
     //  message and thus we can treat it as uninitialised...
     int rc = zmq_msg_init_size (&in_progress, size - 1);
     if (rc != 0 && errno == ENOMEM) {
+        rc = zmq_msg_init (&in_progress);
+        errno_assert (rc == 0);
         decoding_error ();
         return false;
     }