[tex-k] Crash (segmentation fault) from endwrite token

[Karl Berry]

    Subject: [tex-k] Crash (segmentation fault) from endwrite token
    This report is from "user202729" on StackExchange 
    [ ... https://tex.stackexchange.com/questions/609423 ]

Thanks for passing that on. DRF proposed this fix, to simply disallow
\noexpand\endwrite, which seems to be the original source of the problem.
@x [25.369] l.7717 - disallow \noexpand\endwrite
if t>=cs_token_flag then
@y
if (t>=cs_token_flag)and(t<>end_write_token) then
@z

I committed it to TL in r63916, and wrote user202729, and posted on
tex.sx, and added it to newbug.html at
https://tug.org/texmfbug/newbug.html#B155endwrite. First code bug since
the tune-up ...

If any of the other nefarious TeX examples in that tex.sx question seem
like they might be bugs, let me know? I surmise if there is no crash,
Knuth's answer would be "you're getting what you deserve", but hard to
say for sure.

Thanks,
Karl