Load base64 polyfill in IE and friends

lib/private/template.php

@@ -162,6 +162,8 @@ class OC_Template extends \OC\Template\Base {
 			}
 
 			if (\OC::$server->getRequest()->isUserAgent([\OC\AppFramework\Http\Request::USER_AGENT_IE])) {
+				// polyfill for btoa/atob for IE friends
+				OC_Util::addVendorScript('base64/base64');
 				// shim for the davclient.js library
 				\OCP\Util::addScript('files/iedavclient');
 			}