bug#45117: 28.0.50; process-send-string mysteriously exiting non-locally when called from timer

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Eli Zaretskii <eliz@gnu.org>,  45117@debbugs.gnu.org
> Date: Thu, 10 Dec 2020 15:43:16 -0500
> 
> > process_send_string may send things in "bunches", I read in the
> > docstring, but it will not (and should not) be interrupted.
> 
> Indeed, I believe it should not be aborted in the middle by
> `while-no-input` (it would be a bug, because the `process-send-string`
> API doesn't offer any way to know what has been or hasn't been sent in
> that case).

If currently process-send-string isn't protected against
while-no-input, then perhaps we should add such a protection?