fix: skip DataFrame rows without data

[bednar]

Closes #169

Proposed Changes

Skip DataFrame rows without data - all fields are nan

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• A test has been added if appropriate
• pytest tests completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov]

Codecov Report

Merging #170 (2bac660) into master (c8fd3b5) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #170      +/-   ##
==========================================
+ Coverage   89.42%   89.47%   +0.04%     
==========================================
  Files          26       26              
  Lines        1939     1948       +9     
==========================================
+ Hits         1734     1743       +9     
  Misses        205      205              

Impacted Files	Coverage Δ
...fluxdb_client/client/write/dataframe_serializer.py	97.10% <100.00%> (+0.43%)	⬆️

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