Need to OR the type to save the result

0 & anything will always yeilds 0. The type needs to be or'ed with the
current value

Author: nitriques

extension.driver.php

@@ -42,7 +42,7 @@ static public function appendHeaders($type) {
 					$page->addScriptToHead(URL . '/extensions/textboxfield/assets/textboxfield.publish.js', null, false);
 				}
 
-				self::$appendedHeaders &= $type;
+				self::$appendedHeaders |= $type;
 			}
 		}