01488: PHP 8.1 logs deprecation and warning...

PHP Deprecated:  preg_match(): Passing null to parameter #2 ($subject) of type string is deprecated in /path/to/public_html/pmwiki.php on line 1970
PHP Warning:  Undefined variable $anchor in /path/to/public_html/pmwiki.php on line 1975

--- pmwiki-2.3.21.php	2023-02-13 08:36:27.000000000 +0100
+++ pmwiki-2.3.21-patched.php	2023-03-17 11:16:24.002218245 +0100
@@ -1967,12 +1967,12 @@
   if (@$opt['from'] 
       && !MatchPageNames($pagename, FixGlob($opt['from'], '$1*.$2')))
     return '';
-  if (preg_match('/^30[1237]$/', @$opt['status'])) 
+  if (isset($opt['status']) && preg_match('/^30[1237]$/', $opt['status'])) 
      header("HTTP/1.1 {$opt['status']}");
   Redirect($to, "{\$PageUrl}"
     . (IsEnabled($EnableRedirectQuiet, 0) && IsEnabled($opt['quiet'], 0)
       ? '' : "?from=$pagename")
-    . $anchor);
+    . (isset($anchor) ? $anchor : ''));
   exit();
 }