fix(mux): fix the problem that output unreasonable error when exit if enable mux and use Kitex Protobuf

[YangruiEmma]

What type of PR is this?

fix

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fix(mux): 修复当开启 mux 并且使用 Kitex Protobuf 时，在退出时输出不合理的 error 问题

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(Optional) Which issue(s) this PR fixes:

Fixes #894

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[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (dcabd92) 69.05% compared to head (79a3608) 69.07%.

❗ Current head 79a3608 differs from pull request most recent head 3e56005. Consider uploading reports for the commit 3e56005 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #922      +/-   ##
===========================================
+ Coverage    69.05%   69.07%   +0.01%     
===========================================
  Files          238      238              
  Lines        17828    17828              
===========================================
+ Hits         12312    12314       +2     
+ Misses        4411     4410       -1     
+ Partials      1105     1104       -1     

Impacted Files	Coverage Δ
pkg/remote/codec/default_codec.go	75.65% <100.00%> (+1.31%)	⬆️

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