(backup-buffer): Cope if file-modes returns nil.

diff --git a/lisp/files.el b/lisp/files.el
index 3b0fc3e63db91e68671f8d7f1fc07f8af26d54b8..3ec068f953b1ab2a0a36871d0e4114799c792f51 100644 (file)
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -2400,7 +2400,7 @@ BACKUPNAME is the backup file name, which is the old file renamed."
     ;                        (file-symlink-p buffer-file-name)
                              backup-by-copying
                              ;; Don't rename a suid or sgid file.
-                             (< 0 (logand modes #o6000))
+                             (and modes (< 0 (logand modes #o6000)))
                              (and backup-by-copying-when-linked
                                   (> (file-nlinks real-file-name) 1))
                              (and (or backup-by-copying-when-mismatch