Fix checkpoint converter to use arguments before default behavior of checking yaml

[jpmcd]

Script ignores HF_model_path_or_name argument even if supplied and skips to getting model name from yaml file. Test if argument exists before using default approach.

Unfortunately specifying a path causes the script to break.

What does this PR do?

This fixes the faulty default behavior of the converter script.

Fixes # (issue)
No issue

Feature/Issue validation/testing

Please describe the tests that you ran to verify your changes and relevant result summary. Provide instructions so it can be reproduced.
Please also list any relevant details for your test configuration.

No tests needed.

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[jpmcd]

@HamidShojanazeri This commit is tiny enough that you can probably look at the 1 line change + block indent and duplicate it on the main branch. Then just delete this pull request.