get_filename
Description:
Gets the filename for the icon.
If the gtk_icon_lookup_use_builtin flag was passed to lookup_icon, there may be no filename if a builtin icon is returned; in this case, you should use get_builtin_pixbuf.
Parameters:
| this | 
           a IconInfo  | 
      
Returns:
| 
           the filename for the icon, or null if get_builtin_pixbuf should be used instead. The return value is owned by GTK+ and should not be modified or freed.  |