Minor change for sadd command

[hwware]

Update the server.dirty only when it is necessary

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.97%. Comparing base (3884650) to head (8dd15f4).

Additional details and impacted files

@@             Coverage Diff              @@
##           unstable    #2001      +/-   ##
============================================
- Coverage     71.03%   70.97%   -0.07%     
============================================
  Files           123      123              
  Lines         66037    66037              
============================================
- Hits          46911    46867      -44     
- Misses        19126    19170      +44     

Files with missing lines	Coverage Δ
src/t_set.c	97.84% <100.00%> (ø)

... and 8 files with indirect coverage changes

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[hpatro]

If the added variable is zero, it will get optimized out by the compiler I believe. I don't think we necessarily need this change for perf. For code clarity we can.