Added the missing quotes on the filename.

apps/files_sharing/get.php

@@ -70,7 +70,7 @@ if ($source !== false) {
 		header("Expires: 0");
 		header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
 		header("Pragma: public");
-		header("Content-Disposition: filename=".basename($source));
+		header('Content-Disposition: filename="'.basename($source).'"');
 		header("Content-Type: " . $mimetype);
 		header("Content-Length: " . OC_Filesystem::filesize($source));
 		//download the file