fixed some missing conversion in tuh.convert implementation

[keighrim]

fixes #312

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.59%. Comparing base (364af05) to head (2d8bc0f).
Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
mmif/utils/timeunit_helper.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #315      +/-   ##
===========================================
+ Coverage    92.50%   92.59%   +0.09%     
===========================================
  Files           10       10              
  Lines         1400     1405       +5     
===========================================
+ Hits          1295     1301       +6     
+ Misses         105      104       -1     

Flag	Coverage Δ
unittests	92.59% <85.71%> (+0.09%)	⬆️

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