bug#26837: Wrong file in "autoloading failed to define" error

[Eli Zaretskii]

> From: Glenn Morris <rgm@gnu.org>
> Cc: agrambot@gmail.com,  26837@debbugs.gnu.org
> Date: Tue, 09 May 2017 19:49:17 -0400
> 
> Eli Zaretskii wrote:
> 
> >> -  whole_buffer = (PT == BEG && ZV == Z);
> >> +  whole_buffer = (BUF_PT (b) == BUF_BEG (b) && BUF_ZV (b) == BUF_Z (b));
> >
> > You are saying that set_buffer_internal didn't do its job?  Of that
> > the call was bypassed?
> 
> When START = nil (eg when called from eval-buffer), set_buffer_internal
> is never called.

What's the use case when this goes together with b not being the
current buffer?