feat: fix lds observe

[aamingaa]

fix lds resource empty and get cache null

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
1 Code Smell

22.2% Coverage
0.0% Duplication

[codecov-commenter]

Codecov Report

Merging #11300 (ec93fa2) into 3.2 (0419f25) will increase coverage by 0.11%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##                3.2   #11300      +/-   ##
============================================
+ Coverage     65.04%   65.15%   +0.11%     
  Complexity       14       14              
============================================
  Files          1479     1485       +6     
  Lines         61745    62101     +356     
  Branches       9045     9107      +62     
============================================
+ Hits          40160    40460     +300     
- Misses        17374    17441      +67     
+ Partials       4211     4200      -11     

Impacted Files	Coverage Δ
...apache/dubbo/registry/xds/util/PilotExchanger.java	0.00% <0.00%> (ø)
...o/registry/xds/util/protocol/AbstractProtocol.java	66.90% <0.00%> (+1.59%)	⬆️
...o/registry/xds/util/protocol/impl/LdsProtocol.java	12.12% <ø> (+0.69%)	⬆️
.../dubbo/rpc/protocol/tri/stream/AbstractStream.java	83.33% <0.00%> (-16.67%)	⬇️
...bo/rpc/protocol/tri/stream/TripleClientStream.java	45.49% <0.00%> (-8.36%)	⬇️
...oting/transport/netty4/NettyConnectionHandler.java	53.19% <0.00%> (-6.39%)	⬇️
...bbo/common/concurrent/CallableSafeInitializer.java	61.90% <0.00%> (-4.77%)	⬇️
...bo/remoting/zookeeper/AbstractZookeeperClient.java	81.60% <0.00%> (-3.45%)	⬇️
.../config/spring/context/DubboSpringInitializer.java	86.74% <0.00%> (-2.41%)	⬇️
...in/java/org/apache/dubbo/rpc/support/RpcUtils.java	59.44% <0.00%> (-1.63%)	⬇️
... and 72 more

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