Fix output decoding in text_generation_utils.generate for bytes
# What does this PR do ?

Some tokenizers don't have attributes `.tokenizer` or `.tokenizer.byte_decoder`, which results in crashing for these tokenizers (e.g., TikTokenizer and probably most tokenizers implemented in NeMo that derived from TokenizerSpec).

This PR improves this logic to:
1. First checking whether the output type is bytes; otherwise we are good.
2. For bytes outputs, safety checking whether tokenizer.tokenizer.byte_decoder; otherwise simply decode the byte array to string.

# Changelog 
- Fix output decoding in text_generation_utils.generate for bytes

# Usage
N/A

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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@MaximumEntropy

# Additional Information
* Related to # (issue)
