Or if the socket exists and no files are provided, don't start the UI, but only on OSX. On Linux it makes no sense to start Geany with no files when a socket is open, so it acts as if `-i` was given. Maybe that should be different on OSX.
One issue would be are all files given in one callback so Geany can safely close after it, or is each file a separate callback in which case you can't tell if you have them all to exit.