get_default_filter
Description:
Gets the filter that will be selected by default in the file chooser dialog.
Parameters:
| this | 
           a file dialog  | 
      
Returns:
| 
           the default filter  | 
      
Gets the filter that will be selected by default in the file chooser dialog.
| this | 
           a file dialog  | 
      
| 
           the default filter  |