为1.2.3版本更新mysql分支，另外现有sql分支代码存在某些错误。

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我注意到mysql分支的代码似乎并未对1.2.3版本新特性做更新，若能更新mysql分支，我将不胜感激。

另外，现有的mysql分支代码在用户添加、删除方面存在某些逻辑错误导致无法运行，以下是修复方案：

$ac = $_GET['ac'];
if($ac=='add'){
    $username = $_GET['u'];
    $pwd = $_GET['p'];
    $sql = "select * from rustdesk_users where username ='".$username."'";
    $ret = mysqli_query($conn,$sql);
    if(mysqli_num_rows($ret)==0){
        $pwd2 = md5($pwd.'rustdesk');
        $sql ="INSERT INTO rustdesk_users (username,password,create_time) VALUES ('".$username."','".$pwd2."',".time().");";
        mysqli_query($conn,$sql);
        print_r("添加用户". $username."成功~！");exit();
    }else{
        print_r('<span style="color:red">'.$username."已存在，无需重复添加。</span>");exit();
    } 
}
if($ac=='del'){
    $username = $_GET['u'];
    $pwd = $_GET['p'];
    $pwd2 = md5($pwd.'rustdesk');
    $sql = "select * from rustdesk_users where username='".$username."' and password='".$pwd2."'"; 
    $ret = mysqli_query($conn,$sql);
    if($ret = mysqli_fetch_assoc($ret)){ 
    #删除用户对应的tag
    $sql = "delete from rustdesk_tags where uid=".$ret['id'];
    mysqli_query($conn,$sql);
    #删除用户对应的设备信息
    $sql = "delete from rustdesk_peers where uid=".$ret['id'];
    mysqli_query($conn,$sql);
        $sql ="delete  from rustdesk_users where username='".$username."'";
        mysqli_query($conn,$sql);
        print_r("删除用户". $username."成功~！");exit();
    }else{
        print_r('<span style="color:red">用户'.$username."不存在，或密码错误。</span>");exit();
    }
}

修复后经测试运行正常：

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