getSecondsBehindMaster sometimes returns epoch instead of seconds

[ebrard]

It seems that getSecondsBehindMaster in BinaryLogClientStatistics sometimes return the epoch value of timestamp instead of the difference timestamp - eventHeader.getTimestamp(), most likely because eventHeader.getTimestamp()=0. Maybe this happen when getSecondsBehindMaster is called right before a new event is seen/fully deserde, in which case an extra test for a zero value would fix it, something like:

    @Override
    public long getSecondsBehindMaster() {
        // because lastEventHeader and timestampOfLastEvent are not guarded by the common lock
        // we may get some "distorted" results, though shouldn't be a problem given the nature of the final value
        long timestamp = timestampOfLastEvent.get();
        EventHeader eventHeader = lastEventHeader.get();
        if (timestamp == 0 || eventHeader == null ||  eventHeader.getTimestamp() == 0) {
            return -1;
        }
        return (timestamp - eventHeader.getTimestamp()) / 1000;
    }