Problem: pgm_sender does not initialise all its class variables

Solution: do it to silence static analysis warnings

src/pgm_sender.cpp

@@ -51,6 +51,10 @@ zmq::pgm_sender_t::pgm_sender_t (io_thread_t *parent_,
     more_flag (false),
     pgm_socket (false, options_),
     options (options_),
+    handle (static_cast<handle_t> (NULL)),
+    uplink_handle (static_cast<handle_t> (NULL)),
+    rdata_notify_handle (static_cast<handle_t> (NULL)),
+    pending_notify_handle (static_cast<handle_t> (NULL)),
     out_buffer (NULL),
     out_buffer_size (0),
     write_size (0)