ssb: Show activity for each muxrpc request.

src/ssb.connections.c

@@ -21,6 +21,11 @@ typedef struct _tf_ssb_connections_t
 
 static void _tf_ssb_connections_changed_callback(tf_ssb_t* ssb, tf_ssb_change_t change, tf_ssb_connection_t* connection, void* user_data)
 {
+	if (!connection)
+	{
+		return;
+	}
+
 	tf_ssb_connections_t* connections = user_data;
 	switch (change)
 	{