Fix integer overflow in HttpObjectEncoder when handling chunked encoding and FileRegion > Integer.MAX_VALUE

Motivation:

Due to integer overflow bug, writes of FileRegions to http server pipeline (eg like one from HttpStaticFileServer example) with length greater than Integer.MAX_VALUE are ignored in 1/2 of cases (ie no data gets sent to client)

Modification:

Correctly handle chunk sized > Integer.MAX_VALUE

Result:

Be able to use FileRegion > Integer.MAX_VALUE when using chunked encoding.