Add a NULL check into atspi_event_listener_register_from_callback
Add a NULL check into atspi_event_listener_register_from_callback

gloob/gloob-s-at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core,GNOME/at-spi2-core,gloob/gloob-s-at-spi2-core,gloob/gloob-s-at-spi2-core