bug#33510: 26.1.90; M-x man crashes if invoking man fails

[Eli Zaretskii <eliz@gnu.org>]

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> From: Richard Copley <rcopley@gmail.com>
> Date: Mon, 26 Nov 2018 17:02:33 +0000
> 
> On Mon, 26 Nov 2018 at 16:21, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > From: Richard Copley <rcopley@gmail.com>
>  > Date: Mon, 26 Nov 2018 12:34:41 +0000
>  > 
>  > If invoking 'man' fails, M-x man crashes, with errors:
>  >   error in process sentinel: read-event: Buffer is read-only: #<buffer *Man xyzzy*>
>  >   error in process sentinel: Buffer is read-only: #<buffer *Man xyzzy*>
> 
>  Signaling an error is a far cry from a crash...
> 
> Yes, sorry.
>  
>  > To reproduce from 'emacs -Q':
>  > M-x man RET
>  > xyzzy RET
> 
>  I cannot reproduce this, at least not on GNU/Linux: there, I get
> 
>    Can't find the xyzzy manpage
> 
>  as expected.  On MS-Windows I get this instead:
> 
>    No manual entry for xyzzy.
> 
>  So I think the problem is triggered by something done by the 'man'
>  port you have installed (an MSYS2 'man', perhaps?).  What does it say
>  if you invoke it from the shell prompt?
> 
> There was no "man" on the path. (Sorry, I didn't realize that at the time.)

Ah, okay.  With that, I _can_ reproduce the error.