แก้ไขภาพค่ะเวลาไม่เลือกรูปภาพแล้วกดแก้ไข ภาพที่มีอยู่แล้วจะหายไปต้องทำแบบไหนคะ ภาพถึงจะยังอยู่

<?php
require_once'connect.php';
if(isset($_POST['save']));{
      if(!empty($_FILES['photo']['name'])){
              $filename =  md5($_FILES['photo']['name'].time());
              $ext = explode('.',$_FILES['photo']['name']);
              $dest =  __DIR__.DIRECTORY_SEPARATOR.'images'.DIRECTORY_SEPARATOR.$filename.'.'.$ext[1];
              if(!copy($_FILES['photo']['tmp_name'], $dest)) {
                        echo 'upload Error';
                        exit();
              }
              $photo = $filename.'.'.$ext[1];
       }
       
       $id_employee=$_POST['id_employee'];
		$name=$_POST['name'];
		$divistion=$_POST['divistion'];
		$departmant=$_POST['departmant'];
		$duty=$_POST['duty'];
		$tel=$_POST['tel'];
		$mail=$_POST['mail'];

		
		  if(isset($_POST['id_employee'])) {
			
            $sql = "UPDATE employee SET "
                       . "	id_employee = '$id_employee', "
                       . "	name ='$name', "
                       . "	divistion = '$divistion',"
				       . "	departmant = '$departmant',"
					   .  "duty = '$duty',"
                       . "	tel = '$tel', "
					   . "	mail = '$mail', "
					   . "	photo = '$photo' "
					   . "	WHERE id_employee = ". $_POST['id_employee'];  
		
        }else{

        $sql = "INSERT INTO  employee (id_employee,name,divistion,departmant,duty,tel,mail,photo) "
               . "VALUES('$id_employee',$name,$divistion,$departmant,$duty,$tel,$mail,'$photo')";
        }
		
    mysql_query($sql) or die ('save error');
    header('location:list.php');
}