bug#29918: 26.0.90; serial-term error in process filter

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: 29918@debbugs.gnu.org,  gazally@runbox.com,  larsi@gnus.org
> Date: Thu, 18 Jul 2019 07:22:10 -0400
> 
> >> there is a possibility it prevents correct decoding in case the
> >> terminal receives a utf-8 character in single byte chunks (though
> >> I'm not sure if it's even valid for a program to emit single bytes
> >> like that).
> >
> > I agree.
> 
> I thought of limiting partial to 4, to avoid this possibility, since
> utf-8 characters can be 4 bytes at most (not sure about other encodings
> though).  

I don't understand why limit, if we assume that no program will write
UTF-8 encoded sequences byte-byte.  What am I missing?

In general, I'd prefer the simplest fix, as this is going to be pushed
to the release branch, yes?