Add a test case and fix for transcribing markers over a single audio AAF file

[jchen9]

This PR fixes a problem that is only encountered when a marker is found in a media AAF (e.g. one with audio or video data, and only a single clip as the composition.)

[codecov-commenter]

Codecov Report

Merging #1259 (b48cc68) into main (ebd15cd) will increase coverage by 0.06%.
The diff coverage is 93.33%.

@@            Coverage Diff             @@
##             main    #1259      +/-   ##
==========================================
+ Coverage   86.10%   86.17%   +0.06%     
==========================================
  Files         196      196              
  Lines       19671    19697      +26     
  Branches     2308     2309       +1     
==========================================
+ Hits        16937    16973      +36     
+ Misses       2173     2162      -11     
- Partials      561      562       +1     

Flag	Coverage Δ
py-unittests	86.17% <93.33%> (+0.06%)	⬆️

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Impacted Files	Coverage Δ
...elineio_contrib/adapters/tests/test_aaf_adapter.py	97.86% <90.47%> (-0.23%)	⬇️
...neio_contrib/adapters/advanced_authoring_format.py	81.06% <100.00%> (+0.86%)	⬆️
src/opentimelineio/errorStatus.cpp	44.44% <0.00%> (+3.70%)	⬆️
...pentimelineio-bindings/otio_errorStatusHandler.cpp	70.37% <0.00%> (+5.55%)	⬆️
src/opentimelineio/clip.cpp	80.55% <0.00%> (+8.33%)	⬆️

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[meshula]

lgtm