Fixes #1: Mail key "unsubscribe_confirm" pattern not recognized in _easynews_get_mail_key

easynews.module

@@ -692,10 +692,15 @@ function easynews_mail($key, &$message, $params) {
  * Extracts key and id (if present) from a dynamic mail key.
  */
 function _easynews_get_mail_key($key) {
-  preg_match_all("/([a-z_]*)__(\d*)/", $key, $matches);
+  $allowed_keys = array(
+    'newsletter',
+    'unsubscribe_confirm',
+  );
+  $allowed_keys = implode('|', $allowed_keys);
+  preg_match_all("/({$allowed_keys})(__(\d*))?/", $key, $matches);
   return array(
     'key' => $matches[1][0],
-    'id' => $matches[2][0],
+    'id' => $matches[3][0],
   );
 }