Fix: 主备切换后没有往Kafka发送数据

[sosozhuang]

发生主备切换时，调用canalMQStarter启停对应的destination。

1.1.3版本中在CanalMQStarter判断CanalInstance是否存在，如果此时发生切换，再getWithoutAck获取数据会抛出异常。

    private void worker(String destination, AtomicBoolean destinationRunning) {
        ....
        while (running && destinationRunning.get()) {
            try {
                CanalInstance canalInstance = canalServer.getCanalInstances().get(destination);
                if (canalInstance == null) {
                    try {
                        Thread.sleep(3000);
                    } catch (InterruptedException e) {
                        // ignore
                    }
                    continue;
                }
                ....

                while (running && destinationRunning.get()) {
                    Message message;
                    if (getTimeout != null && getTimeout > 0) {
                        message = canalServer.getWithoutAck(clientIdentity,
                            getBatchSize,
                            getTimeout,
                            TimeUnit.MILLISECONDS);
                    } else {
                        message = canalServer.getWithoutAck(clientIdentity, getBatchSize);
                    }

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[codecov-io]

Codecov Report

Merging #1810 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##             master   #1810   +/-   ##
========================================
  Coverage      5.33%   5.33%           
  Complexity      126     126           
========================================
  Files           265     265           
  Lines         23841   23841           
  Branches       3493    3493           
========================================
  Hits           1272    1272           
  Misses        22357   22357           
  Partials        212     212

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