Returns the number of pages that will be printed.
Note that this value is set during print preparation phase (gtk_print_status_preparing), so this function should never be called before the data generation phase (gtk_print_status_generating_data). You can connect to the status_changed signal and call get_n_pages_to_print when print status is gtk_print_status_generating_data. This is typically used to track the progress of print operation.
the number of pages that will be printed