Problem: Several problems found by Coverity Static Analyzer

Solution: The Coverity Static Code Analyzer was used on libzmq code and found
many issues with uninitialized member variables, some redefinition of variables
hidding previous instances of same variable name and a couple of functions
where return values were not checked, even though all other occurrences were
checked (e.g. init_size() return).

src/udp_engine.cpp

@@ -48,6 +48,11 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
 zmq::udp_engine_t::udp_engine_t() :
     plugged (false),
+	fd(NULL),
+	address(nullptr),
+	send_enabled(false),
+	recv_enabled(false),
+	handle(NULL),
     session(NULL)
 {
 }
@@ -122,7 +127,7 @@ void zmq::udp_engine_t::plug (io_thread_t* io_thread_, session_base_t *session_)
             struct ip_mreq mreq;
             mreq.imr_multiaddr = address->resolved.udp_addr->multicast_ip ();
             mreq.imr_interface = address->resolved.udp_addr->interface_ip ();
-            int rc = setsockopt (fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof (mreq));
+            rc = setsockopt (fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (char*) &mreq, sizeof (mreq));
 #ifdef ZMQ_HAVE_WINDOWS
             wsa_assert (rc != SOCKET_ERROR);
 #else