How to prevent 403, 400 errors URL forwarding? - php

Question

Site works good when user enter any url which doesn't exist and forward request to error controller.
But
If you write a script in url site throw 403 error
If you write some asp codes site throw 400 error
How can i prevent this and forward them to custom 403 and 404 pages? I tried forward with htaccess but i couldn't succeed it.
Another problem:
If you write ANY ascii code in adress bar, bootstrap forward to welcome page (controller ->index.php) .How is possible?
Directory structures, htaccess and bootstrap codes are below. Thank you for any help.
Directory structure:
/config
/libs
-bootstrap.php
/controllers
/models
/views
/public_html
-index.php
htaccess
htaccess
htaccess in main directory
<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule ^$ public_html/ [L]
RewriteRule (.*) public_html/$1 [L]
</IfModule>
htaccess in public_html directory
Options -Indexes
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ index.php?url=$1 [PT,L]
</IfModule>
index.php in public_html
<?php
define('DS', DIRECTORY_SEPARATOR);
define('ROOT', dirname(dirname(__FILE__)));
require_once (ROOT . DS . 'libs' . DS . 'bootstrap.php');
$app = new Bootstrap();
bootstrap.php in libs
<?php
class Bootstrap {
function __construct() {
$url = isset($_GET['url']) ? $_GET['url'] : null;
$url = rtrim($url, '/');
$url = explode('/', $url);
print_r($url);
if (empty($url[0])) {
require '../controllers/index.php';
$controller = new Index();
$controller->index();
return false;
}
$file = '../controllers/' . $url[0] . '.php';
if (file_exists($file)) {
require $file;
} else {
$this->error();
return false;
}
$controller = new $url[0];
// calling methods
if (isset($url[2])) {
if (method_exists($controller, $url[1])) {
$controller->{$url[1]}($url[2]);
} else {
$this->error();
}
} else {
if (isset($url[1])) {
if (method_exists($controller, $url[1])) {
$controller->{$url[1]}();
} else {
$this->error();
}
} else {
$controller->index();
}
}
}
function error() {
require '../controllers/error.php';
$controller = new Error();
$controller->index();
return false;
}
}