[Dubbo-5389] fix null attachment issue when consumer use generic

[shadowmind]

What is the purpose of the change

Fix #5389

Brief changelog

XXXXX

Verifying this change

XXXXX

Follow this checklist to help us incorporate your contribution quickly and easily:

• Make sure there is a GITHUB_issue field for the change (usually before you start working on it). Trivial changes like typos do not require a GITHUB issue. Your pull request should address just this issue, without pulling in other changes - one PR resolves one issue.
• Format the pull request title like [Dubbo-XXX] Fix UnknownException when host config not exist #XXX. Each commit in the pull request should have a meaningful subject line and body.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit-test to verify your logic correction, more mock a little better when cross module dependency exist. If the new feature or significant change is committed, please remember to add sample in dubbo samples project.
• Run mvn clean install -DskipTests=false & mvn clean test-compile failsafe:integration-test to make sure unit-test and integration-test pass.
• If this contribution is large, please follow the Software Donation Guide.

[codecov-io]

Codecov Report

Merging #5390 into 2.6.x will decrease coverage by 0.12%.
The diff coverage is 0%.

@@             Coverage Diff              @@
##              2.6.x    #5390      +/-   ##
============================================
- Coverage     48.19%   48.07%   -0.13%     
+ Complexity     4541     4535       -6     
============================================
  Files           562      562              
  Lines         25689    25692       +3     
  Branches       4594     4594              
============================================
- Hits          12382    12352      -30     
- Misses        11416    11445      +29     
- Partials       1891     1895       +4

Impacted Files	Coverage Δ	Complexity Δ
...va/com/alibaba/dubbo/rpc/filter/GenericFilter.java	0% <0%> (ø)	0 <0> (ø)	⬇️
...ubbo/rpc/protocol/dubbo/ChannelWrappedInvoker.java	37.5% <0%> (-12.5%)	3% <0%> (ø)
...aba/dubbo/remoting/transport/mina/MinaChannel.java	42.25% <0%> (-11.27%)	15% <0%> (-1%)
...ba/dubbo/remoting/transport/netty/NettyClient.java	72.88% <0%> (-10.17%)	12% <0%> (-1%)
...om/alibaba/dubbo/rpc/filter/ActiveLimitFilter.java	83.33% <0%> (-5.56%)	6% <0%> (-1%)
...a/dubbo/remoting/transport/netty/NettyChannel.java	61.25% <0%> (-5%)	20% <0%> (-1%)
...rpc/protocol/dubbo/telnet/InvokeTelnetHandler.java	54.21% <0%> (-3.62%)	13% <0%> (-2%)
...bo/remoting/transport/netty/NettyCodecAdapter.java	53.12% <0%> (-1.57%)	3% <0%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7797074...4c85f25. Read the comment docs.