[tex-k] Wrong fix of bug S950 in TeX (and MF)

[Karl Berry]

Hi Igor - finally back on your report in May 2022 (sorry):

    https://tug.org/pipermail/tex-k/2022-May/003822.html
    As you see, the current fix of bug S950 does not change TeX's behavior

Yes, web2c behavior is the same. Since web2c changes all the
editor-related code, the original bug did not occur there.

Knuth's fix was for the original tex.web, and it does make a difference
there. The bug was originally reported at
https://tex.stackexchange.com/questions/552166 and analyzed by Petr Olsak.
In short, tex.web printed string number zero in this
error-within-error case, that is, this message would appear in tex with
plain.fmt loaded:

You want to edit file ^^@ at line 1

Now it behaves more sensibly.  

    ? e
    You want to edit file h.tex at line 1

That's the desired behavior, seems to me. There is an input file h.tex,
so that's what should get edited.

    Now the behavior becomes as intended:
    ...
    ? e
    Type <return> to proceed, S to scroll future error messages,

I don't see that it's better for the e command to just loop back to the
generic help.

Thanks for the report,
Karl