improvements to geet_commonvoice_data script
# What does this PR do ?

compatibility with MCV versions 2 through8

**Collection**: ASR

# Changelog 
- If tsv file does not include .mp3 extension for files, it is added
- If an mp3 file is empty, it is correctly ignored
- if the archive file is not in the {language}.tar.gz format, it is downloaded in that format anyways for correct downstream processing
- if the archive does not have layered directories (e.g. /version/language/files.tsv), it is correctly processed anyways

# Usage


```python
python get_commonvoice_data.py --data_root /data/temp --log --num_workers=16 --language es -- version cv-corpus-6.1-2020-12-11
python get_commonvoice_data.py --data_root /data/temp --log --num_workers=16 --language es --version cv-corpus-4-2019-12-10
python get_commonvoice_data.py --data_root /data/temp --log --num_workers=16 --language es --version cv-corpus-3
python get_commonvoice_data.py --data_root /data/temp --log --num_workers=16 --language es --version cv-corpus-2
```

# Before your PR is "Ready for review"
**Pre checks**:
- [ ] Make sure you read and followed [Contributor guidelines](https://github.com/NVIDIA/NeMo/blob/main/CONTRIBUTING.md)
- [ ] Did you write any new necessary tests?
- [ ] Did you add or update any necessary documentation?
- [ ] Does the PR affect components that are optional to install? (Ex: Numba, Pynini, Apex etc)
  - [ ] Reviewer: Does the PR have correct import guards for all optional libraries?
  
**PR Type**:
- [ ] New Feature
- [ x] Bugfix
- [ ] Documentation

If you haven't finished some of the above items you can still open "Draft" PR.


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# Additional Information
* Related to # (issue)
