#963612 by chx, sun: Stop notices in templates if comment form doesn't exist.

modules/comment/comment.module

@@ -2334,6 +2334,8 @@ function template_preprocess_comment_wrapper(&$variables) {
   // Provide contextual information.
   $variables['node'] = $variables['content']['#node'];
   $variables['display_mode'] = variable_get('comment_default_mode_' . $variables['node']->type, COMMENT_MODE_THREADED);
+  // The comment form is optional and may not exist.
+  $variables['content'] += array('comment_form' => array());
 }
 
 /**