Port the code to PHP 8.5.

Replace the short open tags and the removed functions (mcrypt, mysql_error,
salt-less crypt). Decode the reCAPTCHA reply as JSON, turn off mysqli
exceptions, drop stripslashes(), and default missing input values.
Fix the misplaced continue in prune_images().

publish/preview.inc.php

@@ -1,4 +1,4 @@
-<?
+<?php
 $result = get_post_data(TRUE, TRUE);
 extract($result[0], EXTR_OVERWRITE);
 
@@ -12,7 +12,9 @@ if (isset($_POST['g-recaptcha-response'])) {
   $captcha_resp = file_get_contents("https://www.google.com/recaptcha/api/siteverify?secret=".urlencode(config('RECAPTCHA_SECRET'))."&response=".
       $captcha."&remoteip=".$_SERVER['REMOTE_ADDR']);
   var_dump($captcha_resp);
-  if ($captcha_resp.success==false) {
+  // PHP 8 treats the bare word "success" as an undefined constant, so decode the JSON reply
+  $captcha_json = json_decode((string)$captcha_resp);
+  if (empty($captcha_json->success)) {
     $validate['captcha'] = 'The words you typed in the captcha were not correct. Please try again.';
     include('./write.inc.php');
     return;
@@ -21,7 +23,7 @@ if (isset($_POST['g-recaptcha-response'])) {
 
 echo '<p>Please review your submission. Once you\'ve finished, please click "Submit" at the bottom of the page, or click "Preview" to check it again.</p>';
 
-if (is_uploaded_file($_FILES['upload']['tmp_name']) && !isset($validate['upload'])) {
+if (is_uploaded_file($_FILES['upload']['tmp_name'] ?? '') &&!isset($validate['upload'])) {
   $tmp_file   = $_FILES['upload']['tmp_name'];
   $upload     = getimagesize($tmp_file);
   $new_file   = $_SERVER['DOCUMENT_ROOT'] . "/graphics" . $tmp_file;