Fix bug in File class with wrong parent:: statement.

File.class.php

@@ -39,7 +39,7 @@ abstract class File
             $this->variants[$size] = new ImageVariant;
         } else {
             if (!is_object($this->variants[$size])) {
-                $this->variants[$size] = parent::getInstance($this->variants[$size]);
+                $this->variants[$size] = self::getInstance($this->variants[$size]);
             }
         }
         return $this->variants[$size];