Php8 fixes for #766 (#769)

* init empty vars to avoid PHP8 warnings

* removed debug output for serendipity_session_destroy()

* init smarty fixed for PHP8

* removed optional parameters for PHP 8

* 2k11 template fixes, maybe updating smarty will solve everything

* init or test undefined variables for PHP 8

* remove only existing files

* make sure string is not empty before comparing the first letter

* check if SMARTY_DIR was already defined

* use mb_language('uni') for unicode

* fixed image filter bug

* Smarty debug fixed in external lib

* fixed archive bug

* fixed entries bug

* updated plugin versions

Co-authored-by: surrim <surrim@happyhydro.org>

include/admin/importers/sunlog.inc.php

@@ -240,7 +240,7 @@ class Serendipity_Import_sunlog extends Serendipity_Import {
         return true;
     }
 
-    function importCategories($parentid = 0, $new_parentid = 0, $sunlogdb) {
+    function importCategories($parentid = 0, $new_parentid = 0, $sunlogdb = null) {
         $where = "WHERE parent = '" . mysqli_escape_string($parentid) . "'";
 
         $res = $this->nativeQuery("SELECT * FROM {$this->data['prefix']}categories