Skip if instances is empty

[nghiaphamhn]

Add validation to skip processing when instances collection is empty to prevent unnecessary execution.

[codecov]

Codecov Report

❌ Patch coverage is 33.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.88%. Comparing base (777d1b7) to head (06d43f6).

Files with missing lines	Patch %	Lines
src/DapperRepository.BulkInsert.cs	33.33%	1 Missing and 1 partial ⚠️
src/DapperRepository.BulkUpdate.cs	33.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #553      +/-   ##
==========================================
- Coverage   65.01%   64.88%   -0.14%     
==========================================
  Files          59       59              
  Lines        1941     1945       +4     
  Branches      381      383       +2     
==========================================
  Hits         1262     1262              
- Misses        568      570       +2     
- Partials      111      113       +2     

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