test: add else and error case for TextDecoder
- add test for https://coverage.nodejs.org/coverage-17e4213987c6ad8d/root/internal/encoding.js.html#L365 missing else path
- add test for https://coverage.nodejs.org/coverage-17e4213987c6ad8d/root/internal/encoding.js.html#L385 missing error case
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
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