Toon error bij empty page

/category.php?nameID=Test&id=3

/category.php?nameID=cat2&id=3

This post doesn't exist

<?php
// BEGIN OF SHOWING CONTENT PAGE
if (isset($_GET['id']))
{
        $naamID = mysql_real_escape_string($_GET['nameID']);
        $id     = mysql_real_escape_string($_GET['id']);
        $idnext = $id + 1;
        $goo    = mysql_query("SELECT * FROM category INNER JOIN post ON category.name = post.cat WHERE post.cat = '" .$naamID. "'") or die(mysql_error());
        $gnn    = mysql_query("SELECT * FROM post WHERE id= $id ") or die(mysql_error());
		$gnnn   = mysql_fetch_assoc($gnn);
        $gooo   = mysql_fetch_assoc($goo);
        if($gooo['youtube'])
        {
                $fullurl1 = $gooo['youtube'];
                $videoid1=substr($fullurl1,-11);       
        ?>
                <h1> <?php echo htmlspecialchars($gooo["title"]); ?> </h1><br />
                <p>
                <a href="/editpost.php?id=<?php echo htmlspecialchars($gooo['id']);?>"><i>Edit this post</i></a><br />
                <iframe width="560" height="315" src="//www.youtube.com/embed/<?php echo htmlspecialchars($videoid1);?>" frameborder="0" allowfullscreen></iframe><br />
                </p>
        <?php }if($gooo['pic']){ ?>
                <p>
                <h1><?php echo htmlspecialchars($gooo["title"]); ?></h1><br />
                <a href="/editpost.php?id=<?php echo htmlspecialchars($gooo['id']);?>"><i>Edit this post</i></a><br />
                <img src="<?php echo htmlspecialchars($gooo["pic"]);?>" style="max-height: auto; max-width: 600px;"/><br>
                </p>
        <?php }
// END OF SHOWING CONTENT PAGE
} else {?>