bug#64121: 28.2; C-SPC not working in term char mode

[Eli Zaretskii]

> From: Al Petrofsky <al@petrofsky.org>
> Date: Sat, 17 Jun 2023 02:26:40 -0400
> Cc: 64121@debbugs.gnu.org
> 
> On Sat, Jun 17, 2023 at 2:12 AM Eli Zaretskii <eliz@gnu.org> wrote:
> 
>  > From: Al Petrofsky <al@petrofsky.org>
>  > Date: Fri, 16 Jun 2023 20:06:57 -0400
>  >
>  >    emacs-28.2 -Q
>  >    M-x term RET RET
>  >    C-SPC
>  >
>  > This should send an ASCII NUL (a zero byte) to the pty, but instead it
>  > displays "Mark set" in the echo area.
> 
>  I cannot reproduce this here: I don't see "Mark set" in the echo area.
> 
>  Maybe this somehow depends on the terminal emulator?  (I use PuTTY.)
> 
> I should have mentioned this bug won't show up if emacs is running in a tty. 
> The bug
> stems from the subtle difference between C-SPC and C-@ input events on 
> graphical
> terminals.  On a tty, C-SPC and C-@ become the same thing before they get to 
> emacs.

Then I'm afraid I cannot evaluate this bug and its proposed solution,
as I don't have access to a platform where I can run a GUI Emacs with
"M-x term" still supported.

Could someone else please reproduce this and review the proposed
changes?  TIA.