bug#20663: page.el (forward-page): Avoid skipping pages

[Eli Zaretskii <eliz@gnu.org>]

> From: Marcin Borkowski <mbork@mbork.pl>
> Date: Sat, 09 Apr 2016 12:13:11 +0200
> Cc: 20663@debbugs.gnu.org
> 
> On 2015-05-26, at 19:14, Pierre Neidhardt <ambrevar@gmail.com> wrote:
> 
> > When `page-delimiter` starts at the beginning of the line and the position is
> > also at the beginning of the line, calling `forward-page` will skip one page.
> >
> > Running `emacs -Q example.txt`:
> >
> > 	M-<
> > 	C-x n p
> > 	M->
> > 	M-1 C-x n p
> >
> > This should bring us from page 1 to page 2, but page 3 gets displayed instead.
> >
> > The attached patch fixes it by changing the code to actually match its
> > surrounding comments.
> 
> Hi Emacs devs,
> 
> could someone take a look at the proposed patch?  It is not installed as
> of GNU Emacs 25.1.50.8 (commit 1e8cd05), and I don't feel competent
> enough to be sure it does not have any adverse side effects.

Maybe I'm missing something, but I don't see the connection between
the description of the bug, the recipe, and the patch.

The description talks about calling forward-page, but the recipe
doesn't call it.  The patch compares page-delimiter with an empty
string, but the default value of page-delimiter is not empty.

So I'm mightily confused by this.  Hopefully, someone will show me
what I'm missing.