fixed downloading of files with spaces in name for Firefox

lib/files.php

@@ -121,7 +121,7 @@ class OC_Files {
 			$filename=$dir.'/'.$files;
 		}
 		if($zip or OC_Filesystem::is_readable($filename)){
-			header('Content-Disposition: attachment; filename='.basename($filename));
+			header('Content-Disposition: attachment; filename="'.basename($filename).'"');
 			header('Content-Transfer-Encoding: binary');
 			header('Expires: 0');
 			header('Cache-Control: must-revalidate, post-check=0, pre-check=0');