[Dubbo-2424] Fix switch-case fall through in ChannelEventRunnable

[biyuhao]

What is the purpose of the change

Fix #2424

Brief changelog

Add missing break statement in ChannelEventRunnable#run

Verifying this change

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[codecov-io]

Codecov Report

Merging #2426 into master will decrease coverage by 0.09%.
The diff coverage is 0%.

@@             Coverage Diff             @@
##             master    #2426     +/-   ##
===========================================
- Coverage     55.14%   55.05%   -0.1%     
+ Complexity     5274     5270      -4     
===========================================
  Files           573      573             
  Lines         25459    25460      +1     
  Branches       4537     4537             
===========================================
- Hits          14039    14016     -23     
- Misses         9327     9349     +22     
- Partials       2093     2095      +2

Impacted Files	Coverage Δ	Complexity Δ
...ing/transport/dispatcher/ChannelEventRunnable.java	79.16% <0%> (-1.69%)	9 <0> (ø)
...he/dubbo/remoting/transport/netty/NettyClient.java	72.88% <0%> (-10.17%)	12% <0%> (-1%)
...apache/dubbo/rpc/protocol/dubbo/FutureAdapter.java	58.06% <0%> (-6.46%)	3% <0%> (ø)
...ng/zookeeper/zkclient/ZkclientZookeeperClient.java	59.52% <0%> (-4.77%)	10% <0%> (ø)
...ubbo/rpc/protocol/dubbo/ChannelWrappedInvoker.java	41.66% <0%> (-4.17%)	3% <0%> (ø)
...rg/apache/dubbo/rpc/protocol/dubbo/DubboCodec.java	59.79% <0%> (-4.13%)	14% <0%> (-2%)
...bo/remoting/transport/netty/NettyCodecAdapter.java	53.12% <0%> (-1.57%)	3% <0%> (ø)
...dubbo/rpc/protocol/dubbo/CallbackServiceCodec.java	77.2% <0%> (-1.48%)	29% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	65% <0%> (-1.25%)	22% <0%> (-1%)
...pache/dubbo/registry/support/AbstractRegistry.java	67.41% <0%> (-1.13%)	62% <0%> (ø)
... and 2 more

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[kun-song]

Good catch!

[diecui1202]

It looks good to me.