[Dubbo-7132] Handle scenario where serviceDiscoveryInvoker is null #7132

[kylixs]

What is the purpose of the change

Fix error in issue: #7132

Brief changelog

Handle scenario where serviceDiscoveryInvoker is null

Verifying this change

Run tests under dubbo-samples/dubbo-samples-metadata-report/dubbo-samples-metadata-report-local-xml

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[codecov-io]

Codecov Report

Merging #7133 (3da3f33) into master (27571a0) will decrease coverage by 0.05%.
The diff coverage is 25.00%.

@@             Coverage Diff              @@
##             master    #7133      +/-   ##
============================================
- Coverage     60.28%   60.22%   -0.06%     
+ Complexity      510      505       -5     
============================================
  Files          1028     1028              
  Lines         41531    41535       +4     
  Branches       6038     6040       +2     
============================================
- Hits          25037    25016      -21     
- Misses        13750    13764      +14     
- Partials       2744     2755      +11     

Impacted Files	Coverage Δ	Complexity Δ
...tegration/InterfaceCompatibleRegistryProtocol.java	42.18% <25.00%> (-1.15%)	0.00 <0.00> (ø)
.../remoting/transport/netty4/NettyServerHandler.java	61.36% <0.00%> (-9.10%)	0.00% <0.00%> (ø%)
...e/dubbo/remoting/transport/netty/NettyChannel.java	52.27% <0.00%> (-7.96%)	19.00% <0.00%> (-2.00%)
...in/java/org/apache/dubbo/common/utils/JVMUtil.java	81.13% <0.00%> (-5.67%)	0.00% <0.00%> (ø%)
.../apache/dubbo/remoting/transport/AbstractPeer.java	63.04% <0.00%> (-4.35%)	0.00% <0.00%> (ø%)
...he/dubbo/remoting/transport/netty/NettyServer.java	70.17% <0.00%> (-3.51%)	8.00% <0.00%> (-1.00%)
...pache/dubbo/registry/support/AbstractRegistry.java	79.25% <0.00%> (-1.86%)	0.00% <0.00%> (ø%)
...a/org/apache/dubbo/monitor/dubbo/DubboMonitor.java	88.57% <0.00%> (-0.96%)	16.00% <0.00%> (-1.00%)
...g/apache/dubbo/registry/consul/ConsulRegistry.java	60.00% <0.00%> (-0.59%)	31.00% <0.00%> (ø%)
...figcenter/file/FileSystemDynamicConfiguration.java	62.38% <0.00%> (-0.48%)	0.00% <0.00%> (ø%)
... and 5 more

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[chickenlj]

I've changed the target branch to 2.7.9-release so that we can get it fixed in 2.7.9