bug#18764: 24.4; electric-indent in *scratch* signals an error

[Eli Zaretskii <eliz@gnu.org>]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: Dmitry Gutov <dgutov@yandex.ru>,  18764@debbugs.gnu.org
> Date: Wed, 20 Jun 2018 20:19:16 -0400
> 
> >> That's going to make user complaints like "why it doesn't indent" or "it 
> >> doesn't indent right" harder to debug and address.
> >
> > IMO, this is a lesser evil.  And if it turns out to be a real problem,
> > we could always add a variable to control whether such errors are
> > silently ignored.
> 
> We can be a little more discriminating than my initial blanket
> `ignore-errors', see commit message in the attached patch:

Fine with me, but I'd prefer a comment in the code explaining why we
catch errors here.

Thanks.