[master] set client to null at LazyConnectExchangeClient close methods

[zrlw]

What is the purpose of the change

fix #8880 on master

• set the client field of LazyConnectExchangeClient to null at the end of close() and close(int timeout) methods
• move close status setting from HeaderExchangeChannel close(timeout) to close()

[codecov-commenter]

Codecov Report

Merging #8882 (90868ed) into master (d1644b7) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master    #8882      +/-   ##
============================================
- Coverage     60.79%   60.77%   -0.02%     
- Complexity      446      449       +3     
============================================
  Files          1100     1100              
  Lines         44433    44435       +2     
  Branches       6471     6471              
============================================
- Hits          27011    27007       -4     
  Misses        14446    14446              
- Partials       2976     2982       +6     

Impacted Files	Coverage Δ
...exchange/support/header/HeaderExchangeChannel.java	78.84% <100.00%> (-1.93%)	⬇️
.../rpc/protocol/dubbo/LazyConnectExchangeClient.java	58.06% <100.00%> (-0.18%)	⬇️
...c/protocol/dubbo/ReferenceCountExchangeClient.java	63.33% <100.00%> (ø)
...in/java/org/apache/dubbo/common/utils/JVMUtil.java	81.13% <0.00%> (-11.33%)	⬇️
...ting/exchange/support/header/HeartbeatHandler.java	83.72% <0.00%> (-9.31%)	⬇️
...port/identifier/BaseServiceMetadataIdentifier.java	53.57% <0.00%> (-3.58%)	⬇️
.../remoting/transport/netty4/NettyClientHandler.java	83.05% <0.00%> (-3.39%)	⬇️
...e/dubbo/remoting/exchange/codec/ExchangeCodec.java	77.64% <0.00%> (-2.44%)	⬇️
...pache/dubbo/remoting/transport/AbstractClient.java	61.42% <0.00%> (-2.15%)	⬇️
...pache/dubbo/registry/support/AbstractRegistry.java	80.37% <0.00%> (-1.12%)	⬇️
... and 11 more

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