crypto/http/http_client.c: Add the check for OPENSSL_strdup

crypto/http/http_client.c: Add the check for OPENSSL_strdup

As the potential failure of the OPENSSL_strdup(), it should
be better to check the return value and return error if fails.

Signed-off-by: Jiasheng Jiang <jiasheng@iscas.ac.cn>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18624)