[ISSUE #7836] flush_behind_bytes wrong in transientStorePoolEnable not enable

[leizhiyuan]

when transientStorePoolEnable not enable, we should not add commit bytes

Which Issue(s) This PR Fixes

Fixes #7836

Brief Description

How Did You Test This Change?

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 42.82%. Comparing base (f2dd5b0) to head (7f0c4cf).

Files	Patch %	Lines
...org/apache/rocketmq/store/DefaultMessageStore.java	0.00%	3 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             develop    #7957      +/-   ##
=============================================
- Coverage      42.85%   42.82%   -0.03%     
+ Complexity     10355    10349       -6     
=============================================
  Files           1270     1270              
  Lines          88594    88596       +2     
  Branches       11393    11393              
=============================================
- Hits           37965    37941      -24     
- Misses         45952    45979      +27     
+ Partials        4677     4676       -1     

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