merge r25128 to release-1.12

git-svn-id: http://framework.zend.com/svn/framework/standard/branches/release-1.12@25129 44c647ce-9c0f-0410-b52a-842ac1e357ba

library/Zend/Http/UserAgent/AbstractDevice.php

@@ -195,7 +195,7 @@ abstract class Zend_Http_UserAgent_AbstractDevice
      */
     public function hasFeature($feature)
     {
-        return (!empty($this->_aFeatures[$feature]));
+        return (isset($this->_aFeatures[$feature]) && !is_null($this->_aFeatures[$feature]));
     }
 
     /**