fix: output "0" at the end of toolbar js when Kint::$enabled_mode is false

Author: kenjis

system/Debug/Toolbar.php

@@ -405,6 +405,7 @@ public function prepare(?RequestInterface $request = null, ?ResponseInterface $r
             $kintScript         = @Kint::dump('');
             Kint::$mode_default = $oldKintMode;
             $kintScript         = substr($kintScript, 0, strpos($kintScript, '</style>') + 8);
+            $kintScript         = ($kintScript === '0') ? '' : $kintScript;
 
             $script = PHP_EOL
                 . '<script type="text/javascript" ' . csp_script_nonce() . ' id="debugbar_loader" '