bug#71927: 29.4; ibuffer-do-isearch and ibuffer-do-isearch-regexp not prompting for input

[Juri Linkov]

> Actually, there's another problem with the way ibuffer-do-isearch is
> currently defined via define-ibuffer-op: the BODY of the definition is a
> call to multi-isearch-buffers, but the BODY is called for each marked
> buffer, not once for all of them, so this command currently calls
> multi-isearch-buffers repeatedly when there are multiple marked buffers.
> This causes multi-isearch-setup to be called while multi-buffer Isearch
> is already in progress, which unfortunately breaks regular Isearch for
> the rest of the session.
>
> To see this effect, invoke ibuffer-do-isearch with two or more marked
> buffers, quit or finish the search (e.g. type C-g), and then try regular
> Isearch with C-s and repeat C-s until wrapping around.  But instead of
> wrapping around as expected, Emacs displays an error:
>
>   Symbol’s function definition is void: nil
>
> A simple solution is to use plain defun for these commands, as follows:

I agree that plain defun would be better.