IndexError: No SlotID: 0

## Bug Report
I am trying to use OTIO to get AAF data with python, I can open some AAF file & work with those with no problem but for some others I get an error.
```
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/aaf2/mobs.py", line 82, in slot_at
raise IndexError("No SlotID: %s" % str(slot_id))
IndexError: No SlotID: 0
```

## To Reproduce

1. Operating System: MacOS 14.2.
2. Python version: 3.9.5
3. Example snippet that demonstrates the issue - if it's a build issue
```
import opentimelineio as otio

timeline = otio.adapters.read_from_file('my_file.aaf')
for clip in timeline.each_clip():
print(clip.name)
```
4. OpenTimelineIO release version or commit hash: OpenTimelineIO 0.14.1 as well as with the branch git+https://github.com/andrewmoore-nz/OpenTimelineIO.git@0d9fb920668556dce3f62662766b8550a8c56243
5. Compiler information:
```
Apple clang version 13.1.6 (clang-1316.0.21.2.5)
Target: x86_64-apple-darwin21.5.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
```

## Expected Behavior
Interact with the clips, tracks, etc, just as the same with other files, this happens with a few files, nothing particular special about those files.

## Screenshots

## Logs
```
Traceback (most recent call last):
File "/Users/diego.dominguez01/Documents/aaf-parser-collab/parsing_aaf.py", line 30, in
my_otio = MyOTIO(file_name=file_name, path=path, file_index=index)
File "/Users/diego.dominguez01/Documents/aaf-parser-collab/components/otio_component.py", line 19, in __init__
self.my_otio = self.reading_file()
File "/Users/diego.dominguez01/Documents/aaf-parser-collab/components/otio_component.py", line 35, in reading_file
return otio.adapters.read_from_file(file_path)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio/adapters/__init__.py", line 143, in read_from_file
return adapter.read_from_file(
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio/adapters/adapter.py", line 145, in read_from_file
result = self._execute_function(
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio/plugins/python_plugin.py", line 174, in _execute_function
return (getattr(self.module(), func_name)(**kwargs))
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 1568, in read_from_file
result = _transcribe(mobs_to_transcribe, parents=list(), edit_rate=None)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 827, in _transcribe
result.append(_transcribe(child, parents + [item], edit_rate, indent + 2))
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 447, in _transcribe
track = _transcribe(slot, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 673, in _transcribe
child = _transcribe(item.segment, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 659, in _transcribe
child = _transcribe(component, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 665, in _transcribe
result = _transcribe_operation_group(item, parents, metadata,
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 1154, in _transcribe_operation_group
child = _transcribe(segment, parents + [item], edit_rate, indent)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 659, in _transcribe
child = _transcribe(component, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 542, in _transcribe
mastermob_child = _transcribe(mastermob, list(), edit_rate, indent)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 447, in _transcribe
track = _transcribe(slot, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 673, in _transcribe
child = _transcribe(item.segment, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 659, in _transcribe
child = _transcribe(component, parents + [item], edit_rate, indent + 2)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 476, in _transcribe
mobs = _find_timecode_mobs(item)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/opentimelineio_contrib/adapters/advanced_authoring_format.py", line 304, in _find_timecode_mobs
for c in item.walk():
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/aaf2/components.py", line 201, in walk
for item in clip.walk():
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/aaf2/components.py", line 183, in walk
if not self.slot:
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/aaf2/components.py", line 157, in slot
return mob.slot_at(slot_id)
File "/Users/diego.dominguez01/Documents/pyenv/marvel_proj/lib/python3.9/site-packages/aaf2/mobs.py", line 82, in slot_at
raise IndexError("No SlotID: %s" % str(slot_id))
IndexError: No SlotID: 0
```

Start by reproducing the failure with the reported AAF input and read opentimelineio_contrib/adapters/advanced_authoring_format.py around read_from_file, _transcribe, and _find_timecode_mobs. Trace the IndexError through aaf2/components.py and aaf2/mobs.py, then verify that the affected AAF files can be read and their clips iterated without the missing SlotID error.

Written by the indexing model from the issue text.