Motivation:
This fixes issue 3168 where HttpObjectAggregator does not suppress
channelReadComplete() when aggregation is not yet finished.
Modifications:
Ignore channelReadComplete until a message completes aggregation.
MessageAggregator currently tracks the currentMessage being aggregated.
This variable transitions to non-null when aggregation begins and back
to null when aggregation completes or fails. When the currentMessage is
null, it is safe to issue a channelReadComplete because the
corresponding channelRead will have completed aggregation.
Result:
channelReadComplete will only fire one time on each completed message
aggregation.
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