GUACAMOLE-470: Fix crash when X11 color is not found.
GUACAMOLE-470: Fix crash when X11 color is not found.

Fix a crash when an X11 color name is not found. The variable to
null-check should be `found`, not `color`.

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