Fix buffer leak introduced by #2462

Motivation:
Because of not correctly release a buffer before null out the reference a memory leak shows up.

Modifications:
Correct call buffer.release() before null out reference.

Result:
No more leak
Adding short-curcuit option for CORS

Motivation:
CORS request are currently processed, and potentially failed, after the
target ChannelHandler(s) have been invoked. This might not be desired, for
example a HTTP PUT or POST might have been performed.

Modifications:
Added a shortCurcuit option to CorsConfig which when set will
cause a validation of the HTTP request's 'Origin' header and verify that
it is valid according to the configuration. If found invalid an 403
"Forbidden" response will be returned and not further processing will
take place.

This is indeed no help for non browser request, like using curl, which
can set the 'Origin' header.

Result:
Users can now configure if the 'Origin' header should be validated
upfront and have the request rejected before any further processing
takes place.