Fix bug with pre HTML Purifier 3.1.0rc1

CHANGELOG.txt

+5.x-1.3, released 2008-05-12
+- Bugfix release, fix fatal error on configure page when using version
+  of HTML Purifier earlier than 3.1.0rc1
+
 5.x-1.2, released 2008-05-11
 # WARNING: REALLY, the last Drupal 5.x release. We decided to do another release
   because the previous one was lacking in some major features.

htmlpurifier.module

@@ -109,7 +109,7 @@ function _htmlpurifier_settings($format) {
     if (!$enabled) {
       $form['htmlpurifier']['htmlpurifier_allowedhtml']["htmlpurifier_allowedhtml_$format"]['#disabled'] = TRUE;
     }
-    if (!defined('HTMLPurifier::VERSION') && version_compare(HTMLPurifier::VERSION, '3.1.0-dev', '>=')) {
+    if (defined('HTMLPurifier::VERSION') && version_compare(HTMLPurifier::VERSION, '3.1.0-dev', '>=')) {
       $form['htmlpurifier']['htmlpurifier_allowedhtml']["htmlpurifier_forbiddenelements_$format"] = array(
         '#type' => 'textarea',
         '#title' => t('Forbidden elements'),