launcher-gtk: Add missing NULL at the end of gdk_pixbuf_save_to_stream()
launcher-gtk: Add missing NULL at the end of gdk_pixbuf_save_to_stream()

gdk_pixbuf_save_to_stream() is a vararg function whose vararg parameters
have to be NULL-terminated.

GNOME/libchamplain,GNOME/libchamplain