fix at PHP 7.0 not working migrating vfs from db to filesystem (filemanager/cli.php migrate-db2fs)

can not unset variable bind to column, as it looses its bind

api/src/Vfs/Sqlfs/Utils.php

@@ -55,7 +55,7 @@ class Utils extends StreamWrapper
 					$content = fopen('php://temp', 'wb');
 					fwrite($content, $fs_content);
 					fseek($content, 0, SEEK_SET);
-					unset($fs_content);
+					$fs_content = '';	// can NOT unset it, at least in PHP 7 it looses bind to column!
 				}
 				else
 				{