Gets the id of the stock icon being displayed by the #GtkStatusIcon.
The storage type of the status icon must be %GTK_IMAGE_EMPTY or
%GTK_IMAGE_STOCK (see gtk_status_icon_get_storage_type()).
The returned string is owned by the #GtkStatusIcon and should not
be freed or modified.
Gets the id of the stock icon being displayed by the #GtkStatusIcon. The storage type of the status icon must be %GTK_IMAGE_EMPTY or %GTK_IMAGE_STOCK (see gtk_status_icon_get_storage_type()). The returned string is owned by the #GtkStatusIcon and should not be freed or modified.