http2: replace unreachable error with assertion
"That particular emit('error', ...)
is largely defensively coded and
should not ever actually happen." Sounds like an assertion rather than
an error event. The code in question has no test coverage because it is
believed to be unreachable.
Fixes: https://github.com/nodejs/node/issues/20673
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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