Fix code scanning alert #5: Unsigned difference expression compared to zero

[HTHou]

Fixes https://github.com/apache/tsfile/security/code-scanning/5

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 61.67%. Comparing base (1686cff) to head (f9ff4d8). Report is 1 commits behind head on develop.

Files with missing lines	Patch %	Lines
cpp/src/reader/bloom_filter.cc	0.00%	0 Missing and 1 partial :warning:

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #249   +/-   ##
========================================
  Coverage    61.67%   61.67%           
========================================
  Files          491      491           
  Lines        32248    32248           
  Branches      4226     4226           
========================================
  Hits         19889    19889           
  Misses       11912    11912           
  Partials       447      447           

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