http_client: fix header_lookup() to honor the header/body boundery (#823)
http_client: fix header_lookup() to honor the header/body boundery (#823)

header_lookup() has a bug that it goes over the boundary line and
finds matches in the body part.

This patch fixes the bug by limiting its search scope to the HTTP
header section.

Signed-off-by: Fujimoto Seiji <ef879192bb1e41d519c82cf76440dc8e9a530806@clear-code.com>
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