Avoid useless byte array allocation for VarChunkV4Reader StringMV

[wirybeaver]

The title says it all.

Benchmarking: TBD.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.17%. Comparing base (59551e4) to head (c5e7785).
Report is 345 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #12978      +/-   ##
============================================
+ Coverage     61.75%   62.17%   +0.42%     
+ Complexity      207      198       -9     
============================================
  Files          2436     2502      +66     
  Lines        133233   136503    +3270     
  Branches      20636    21128     +492     
============================================
+ Hits          82274    84872    +2598     
- Misses        44911    45352     +441     
- Partials       6048     6279     +231     

Flag	Coverage Δ
custom-integration1	<0.01% <0.00%> (-0.01%)	⬇️
integration	<0.01% <0.00%> (-0.01%)	⬇️
integration1	<0.01% <0.00%> (-0.01%)	⬇️
integration2	0.00% <0.00%> (ø)
java-11	62.09% <100.00%> (+0.38%)	⬆️
java-21	62.05% <100.00%> (+0.43%)	⬆️
skip-bytebuffers-false	62.14% <100.00%> (+0.39%)	⬆️
skip-bytebuffers-true	35.03% <0.00%> (+7.30%)	⬆️
temurin	62.17% <100.00%> (+0.42%)	⬆️
unittests	62.17% <100.00%> (+0.42%)	⬆️
unittests1	46.72% <0.00%> (-0.17%)	⬇️
unittests2	27.94% <100.00%> (+0.21%)	⬆️

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[Jackie-Jiang]

Nice!