GUACAMOLE-184: Only send contents of surface if non-empty.
GUACAMOLE-184: Only send contents of surface if non-empty.

apache/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server,apache/guacamole-server,glyptodon/guacamole-server,mike-jumper/incubator-guacamole-server,mike-jumper/incubator-guacamole-server