changes on html_select_date

I made a change on the file `function.html_select_date.php':
after version 1.3 we have the day_empty, month_empty and year_empty 
attribute.
I think if the time attribute is empty and the day_empty or month_empty 
or year_empty attribute are set we should left blank the generated field.
Follow my patch:

if(empty($time) and (!is_null($day_empty) or !is_null($month_empty) or 
!is_null($year_empty))){
   $time = '--';
}else{
   $time = strftime('%Y-%m-%d', smarty_make_timestamp($time));
}



-- 
Everton Luis Berz
Nucleo de Sistemas :: FACCAT - Faculdades de Taquara
+55 51 541 6600 - R.647
ICQ 7807919