content_encoding: ignore duplicate chunked encoding

- ignore duplicate "chunked" transfer-encodings from
a server to accomodate for broken implementations
- add test1482 and test14

content_encoding: ignore duplicate chunked encoding

- ignore duplicate "chunked" transfer-encodings from
a server to accomodate for broken implementations
- add test1482 and test1483

Reported-by: Mel Zuser
Fixes #13451
Closes #13461

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