Fix regression introduced by 4c7fa950cc4f4c52eeaae5887335b1f3047592f8

- Some promises were not fulfilled when SSLEngine produces 0 bytes.
Also allow to disable header validation via HttpServerCodec and HttpClientCodec. Related to [#1981]
[#1982] Limit the usage of ThreadLocal.get() for performance reasons
Merge remote-tracking branch: upstream/master