bug#36573: 26.1; bufferpos-to-filepos assumes coding-system-eol-type gives integer

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: rswarbrick@gmail.com,  36573@debbugs.gnu.org
> Date: Thu, 12 Aug 2021 14:54:51 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I think, since these cases are very rare, it should be okay to assume
> > the -unix EOL type when this happens, and document that if this is the
> > case, the result could be an approximation even if the exact result
> > was requested.
> 
> It is a rare odd corner case, but I think erroring out is a better
> solution here than having to document this.  :-)  `exact' meaning
> "exact" is easier conceptually.

Fine with me, but I think we will still need to say in the doc string
something like

  It is an error to request the `exact' method when the buffer's EOL
  format is not yet decided.