Fix incorrect calculation in indexTree.treePosToPath operation

[humdrum]

What this PR does / why we need it:

• Fix incorrect calculation in indexTree.treePosToPath operation yorkie-js-sdk#751
  Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

Attention: 212 lines in your changes are missing coverage. Please review.

Comparison is base (9f70093) 42.45% compared to head (955f7bd) 42.30%.

Files	Patch %	Lines
Tests/Integration/TreeIntegrationTests.swift	0.00%	122 Missing ⚠️
Tests/Integration/IntegrationHelper.swift	0.00%	90 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
- Coverage   42.45%   42.30%   -0.15%     
==========================================
  Files         104      104              
  Lines       24328    24425      +97     
==========================================
+ Hits        10328    10333       +5     
- Misses      14000    14092      +92     

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