Omitting optional argument of `w3m-tab-previous-buffer' causes an error

[IRIE Shinsuke <irieshinsuke@xxxxxxxxxxx>]

Hi,

I found that a function `w3m-tab-previous-buffer' causes an error
"Wrong type argument: number-or-marker-p, nil" if it is called with
no arguments non-interactively like "(w3m-tab-previous-buffer)".

Currently the code is as follows:

(defun w3m-tab-previous-buffer (&optional n event)
  "Turn N pages of emacs-w3m buffers behind."
  (interactive (list (prefix-numeric-value current-prefix-arg)
		     last-command-event))
  (w3m-tab-next-buffer (- n) event))

Here, "(- n)" cannot be calculated if N is omitted. To avoid the error,
it should be modified as:

(defun w3m-tab-previous-buffer (&optional n event)
  "Turn N pages of emacs-w3m buffers behind."
  (interactive (list (prefix-numeric-value current-prefix-arg)
		     last-command-event))
  (w3m-tab-next-buffer (- (or n 1)) event))

Thanks.

IRIE Shinsuke