Fixes the issue where data with only timestamps could not be inserted

[ColinLeeo]

In this pr:
fix the issue when data with only timestamp could not be inserted and queried.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.

Project coverage is 65.96%. Comparing base (de166a7) to head (25e47f0).
Report is 2 commits behind head on develop.

Files with missing lines	Patch %	Lines
cpp/src/writer/tsfile_writer.cc	80.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #525      +/-   ##
===========================================
+ Coverage    65.93%   65.96%   +0.02%     
===========================================
  Files          566      566              
  Lines        33596    33614      +18     
  Branches      4729     4734       +5     
===========================================
+ Hits         22153    22174      +21     
+ Misses       10768    10767       -1     
+ Partials       675      673       -2     

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